Optical element, aberration correcting element, light converging element, objective optical system, optical pickup device, and optical information recording reproducing device

ABSTRACT

An optical system for use in an optical pickup apparatus comprises a first optical surface having a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and a second optical surface having a diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones are divided by a stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

BACKGROUND OF THE INVENTION

The present invention relates to an optical element for an opticalpickup device, aberration correcting element, light converging element,objective optical system, optical pickup device using these opticalelements, and optical information recording reproducing device.

Recently, in the optical pickup device, a tendency to reduce thewavelength of a laser light source used as the light source forrecording the information into an optical disk, is advanced, forexample, a laser light source of a wavelength 405 nm such as a blueviolet semiconductor laser or a blue violet SHG laser in which thewavelength conversion of the infrared semiconductor laser is conductedby using the second harmonics generation, is being put to practical use.

When these blue violet laser light sources are used, in the case wherean objective lens whose numerical aperture (NA) is the same as that ofDVD (digital versatile disk) is used, the information of 15-20 GB can berecorded in an optical disk of 12 cm diameter, and in the case where NAof the objective lens is increased to 0.85, the information of 23-25 GBcan be recorded in the optical disk of 12 cm diameter. Hereinafter, inthe present specification, the optical disk and optical magnetic diskusing the blue violet laser light source are generally called as “highdensity optical disk”.

Hereupon, in the high density optical disk using the objective lens ofNA 0.85, because a coma generated caused by the skew of the optical diskis increased, a protective layer is designed thinner than in DVD (0.1 mmto 0.6 mm of DVD), and an amount of the coma due to the skew is reduced.

Hereupon, only by a fact that the information can be appropriatelyrecorded/reproduced for such a high density optical disk, it can not besaid that a value as a product of an optical disk player is sufficient.In the present time, when the actuality that DVD and CD (compact disk)in which various kinds of information are recorded, are sold in amarket, is taken into account, it is not sufficient only by a fact thatthe information can be recorded/reproduced for the high density opticaldisk, but, for example, when it is structured in such a manner that,also to DVD or CD which is owned by the user, the information can beappropriately recorded/reproduced in the same manner, it leads to anincrease of the product value as an optical disk player for a highdensity optical disk. From such a background, in the optical pickupdevice mounted on the optical disk player for the high density opticaldisk, it is desired that it has the performance by which the informationcan be appropriately recorded/reproduced, while keeping theinterchangeability also for any one of the high density optical disk andDVD, further, CD.

A method is considered by which the optical parts for the high densityoptical disk and the optical system for DVD or CD are selectivelyswitched corresponding to the recording density of the optical disk forwhich the information is recorded/reproduced, as a method by which theinformation is appropriately recorded/reproduced while keeping theinterchangeability also for any one of the high density optical disk andDVD, further, CD, however, because a plurality of optical systems arenecessary, it is disadvantageous for size-reduction, further, the costis increased.

Accordingly, for the purpose of simplification of the structure of theoptical pickup device and cost-reduction, also in the optical pickupdevice having the interchangeability, it is preferable that the opticalsystem for the high density optical disk and the optical system for DVDor CD are in common with each other, and the number of optical partsconstituting the optical pickup device is reduced as largely aspossible.

As the objective optical system for the optical system which can be usedin common with a plurality of kinds of optical disks whose recordingdensity is different each other, a technology by which the ring shapedzone structure around the optical axis as written in Patent Documents 1and 2, is provided on the lens surface, and in respective ring shapedzones, a plurality of concave and convex structures are formed, is wellknown.

(Patent Document 1) Tokkaihei 9-306018

(Patent Document 2) Tokkai 2002-277732

The technology written in 2 above-described Patent Documents is atechnology in which, when the depth of a stepped section of theconcave-convex structure formed in the ring shaped zone is made a depthso that practically the phase difference is not added in mutualadjoining concave-convex structures to the wavelength (for example, λ1)of either one of the recording/reproducing wavelength λ1 of DVD or therecording/reproducing wavelength λ2 of CD, it is made in such a mannerthat, by the concave-convex structure, the phase difference is givenonly to the other side wavelength (for example, λ2).

Further, by the number of concave-convex structures formed in each ofring shaped zones, because when the light flux of wavelength λ2 passesthe ring shaped zone structure, the phase difference of integer times ofthe wavelength is given in mutual adjoining ring shaped zones, only thelight flux of wavelength λ2 is diffracted by the ring-shaped zonestructure. The concave-convex structure formed in each ring shaped zonein this case, is set so that both transmission factors (diffractionefficiency) for the wavelength λ1 and the wavelength λ2 are largelysecured.

In the objective optical system written in Patent Document 1, when thelight flux of the wavelength λ2 is diffracted by the ring-shaped zonestructure, the light flux of the wavelength λ2 is projected as thediverging light flux so that spherical aberrations generated due to thedifference of protective layer thickness between DVD and CD arecancelled, and in the objective optical system in Patent Document 2,when the light flux of the wavelength λ2 is diffracted by the ringshaped zone structure, because the spherical aberration by whichspherical aberrations generated due to the difference of protectivelayer thickness between DVD and CD are cancelled, is added to the lightflux of the wavelength λ2, recording/reproducing of the information forthe DVD and CD can be conducted by a common objective optical system.

Both of technologies disclosed in Patent Documents 1 and 2 aretechnologies by which the interchange between 2 kinds of optical disksof DVD and CD is realized, and because there is no disclosure for theoptimum ring shaped zone structure (for example, the number ofconcave-convex structures formed in each ring shaped zone) for thepurpose in which, for the recording/reproducing wavelength (the vicinityof 400 nm) of the high density optical disk and therecording/reproducing wavelength (the vicinity of 650 nm) of DVD, thespherical aberrations generated due to the difference of the protectivelayer thickness between the high density optical disk and DVD arecorrected, and the high transmission factor (diffraction efficiency) issecured, for the purpose in which the interchange between the highdensity optical disk and DVD is realized, it is difficult that thetechnologies disclosed in the above-described Patent Documents areapplied as they are.

Further, in order to conduct the recording/reproducing of theinformation by using the common objective optical system on the highdensity optical disk and DVD, as described above, other than thespherical aberration generated due to the difference of the protectivelayer thickness between the high density optical disk and DVD, it isnecessary that problems proper to the high density optical disk aresolved.

Problems proper to the high density optical disk are (1) the chromaticaberration accompanied by a reduction of wavelength of the laser opticalsource (2) the spherical aberration change accompanied by an increase ofnumerical aperture. In them, (1) is the problem actualized for thereason that the wavelength dispersion (a change of refractive index to aminute wavelength change) of optical materials is large in the blueviolet wavelength area. When the mode is switched for the optical disk,from the reproducing of the information to the recording or from therecording of the information to the reproducing, because the output ofthe semiconductor laser light source is changed, the oscillationwavelength is changed (so-called mode-hopping). This wavelength changeis about several nm, however, because the wavelength dispersion is largein the blue violet wavelength area, while the objective optical systemis focused again, it is in the de-focus condition, and the adequaterecording/reproducing characteristic is not obtained.

Further, (2) is a problem actualized for the reason that the sphericalaberration generated in the objective optical system is increased inproportion to fourth power of the numerical aperture. In the objectiveoptical system of high numerical aperture, because the sphericalaberration when the wavelength of the incident light flux is changed, isincreased, the allowance for the wavelength of the laser light sourcebecomes severe. Particularly, because there is an influence of thewavelength dispersion in the blue violet wavelength area, this problemis more actualized. Further, in order to reduce a production cost, it iseffective that the objective optical system is formed of a plastic lens,however, because the spherical aberration generated due to therefractive index change accompanied by the temperature change isincreased, when the temperature in the optical pickup device is changed,the recording/reproducing characteristic of the information for the highdensity optical disk is interfered.

SUMMARY OF THE INVENTION

The aspect of the present invention considers the above-describedproblems, and the object of the present invention is to provide anoptical element for an optical pickup device by which the recordingand/or reproducing of the information can be appropriately conducted ona plurality kinds of optical information recording media, including thehigh density optical disk and DVD using the blue violet laser lightsource, whose using wavelengths are different, aberration correctingelement for the optical pickup device, light converging element for theoptical pickup device, objective optical system, optical pickup device,and optical information recording reproducing device.

(1) An optical system for use in an optical pickup apparatus in whichreproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first wavelength λ1emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising:

a first optical surface having a superposition type diffractivestructure including a plurality of ring-shaped zones which are formedconcentrically around an optical axis, wherein each ring-shaped zone iscomposed of a plurality of stepped sections stepwise, and

a second optical surface having a diffractive structure including aplurality of ring-shaped zones which are formed concentrically around anoptical axis, wherein each of the plurality of ring-shaped zones aredivided by a stepped section to generate a diffractive light ray ofdiffractive order whose absolute value is not small than 1 for the lightflux.

(2) An optical system for use in an optical pickup apparatus in whichreproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first |wavelengthλ1 emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising:

a first optical surface having a superposition type diffractivestructure including a plurality of ring-shaped zones which are formedconcentrically around an optical axis, wherein each ring-shaped zone iscomposed of a plurality of stepped sections stepwise, and

a second optical surface having an optical path difference providingstructure including a plurality of ring-shaped zones which are formedconcentrically around an optical axis, wherein each of the plurality ofring-shaped zones is divided by a stepped section so as to provide apredetermined optical path difference, and wherein an optical pathlength of each of the plurality of ring-shaped zones changes in responseto a height from the optical axis.

(3) An optical system for use in an optical pickup apparatus in whichreproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first wavelength λ1emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising:

a correcting optical system;

a light converging element to converge a light flux having a wavelengthλ1 emitted from the correcting optical system on an informationrecording plane of the first optical information recording medium and toconverge a light flux having a wavelength λ2 emitted from the correctingoptical system on an information recording plane of the second opticalinformation recording medium;

wherein an optical surface of the correcting optical system has aplurality of optical functional zones, and a superposition typediffractive structure is formed within one of the plurality of opticalfunctional zones such that a plurality of ring-shaped zones are formedconcentrically around the optical axis and plural stepped sectionsshaped stepwise are formed within each ring-shaped zone.(4) A correcting optical system for use in an optical pickup apparatusin which reproducing and/or recording information is conducted for afirst optical information recording medium equipped with a protectivelayer having a thickness t1 by using a light flux having a firstwavelength λ1 emitted from a first light source and reproducing and/orrecording information is conducted for a second optical informationrecording medium equipped with a protective layer having a thickness t2(t2≧t1) by using a light flux having a second wavelength λ2 (λ2>λ1)emitted from a second light source, wherein the correcting opticalsystem is provided on an optical path between both of the first andsecond light sources and a light converging element to converge a lightflux having the first wavelength λ1 emitted from the first light sourceand a light flux having the second wavelength λ2 emitted from the secondlight source respectively onto an information recording plane of thefirst and second optical information recording mediums; and thecorrecting optical system comprising:

an optical surface having a plurality of ring-shaped optical functionalzones, and a superposition type diffractive structure is formed on oneof the plurality of optical functional zones such that a plurality ofring-shaped zones are formed concentrically around the optical axis andplural stepped sections shaped stepwise are formed within eachring-shaped zone.

(5) A light converging element for use in an optical pickup apparatus inwhich reproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first wavelength λ1emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising:

an optical surface of the light converging element having a plurality ofoptical functional zones, and a superposition type diffractive structureis formed within one of the plurality of optical functional zones suchthat a plurality of ring-shaped zones are formed around the optical axisand plural stepped sections shaped stepwise are formed within eachring-shaped zone.

(6) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1for conducting recording and/or reproducing information for a firstinformation recording medium equipped with a protective substrate havinga thickness t1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1) for conducting recording and/or reproducing information for asecond information recording medium equipped with a protective substratehaving a thickness t2 (t2≧t1);

a third light source to emit a light flux having a third wavelength λ3(λ3>λ2>λ1) for conducting recording and/or reproducing information for athird information recording medium equipped with a protective substratehaving a thickness t3 (t3≧t2);

an objective optical system to converge a light flux having thewavelength λ1, λ2 or λ3 onto the first, second or third informationrecording medium respectively;

a diaphragm;

a driving device to drive the objective system and the diaphragm as oneunit in a direction perpendicular to the optical axis;

an entering devise to make at least one light flux among light fluxeshaving the first, second and third wavelengths λ1, λ2 and λ3 enter innot parallel to the optical axis into the objective optical system; and

a coma aberration correcting element provided between the objective lensand a light source to emit a light flux which enters in not parallel tothe optical axis into the objective optical system and to reduce a comaaberration generated when the objective optical system is driven in thedirection perpendicular to the optical axis by the driving device;

wherein an optical surface of the objective optical system has aplurality of optical functional zones, and a superposition typediffractive structure is formed within the optical functional zoneincluding an optical axis of the plurality of optical functional zonessuch that a plurality of ring-shaped zones are formed around the opticalaxis and plural stepped sections shaped stepwise are formed within eachring-shaped zone.

(7) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1for conducting recording and/or reproducing information for a firstinformation recording medium equipped with a protective substrate havinga thickness t1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1) for conducting recording and/or reproducing information for asecond information recording medium equipped with a protective substratehaving a thickness t2 (t2≧t1);

a third light source to emit a light flux having a third wavelength λ3(λ3>λ2>λ1) for conducting recording and/or reproducing information for athird information recording medium equipped with a protective substratehaving a thickness t3 (t3≧t2);

an objective optical system to converge a light flux having thewavelength λ1, λ2 or λ3 onto the first, second or third informationrecording medium respectively, wherein an optical surface of theobjective optical system has a plurality of optical functional zones,and a superposition type diffractive structure is formed within anoptical functional zone including an optical axis of the plurality ofoptical functional zones such that a plurality of ring-shaped zones areformed around the optical axis and plural stepped sections shapedstepwise are formed within each ring-shaped zone;

an entering device to enter at least two light fluxes with respectivedifferent magnifications into the objective optical system among lightfluxes having the first, second and third wavelengths λ1, λ2 and λ3;

an divergent angle converting element having an optical surfaceincluding a superposition type diffractive structure, wherein thesuperposition type diffractive structure includes a plurality ofring-shaped zones which are formed concentrically around an opticalaxis, wherein each ring-shaped zone is composed of a plurality ofstepped section stepwise, the divergent angle converting element toconvert a divergent angle of at least a light flux having one of thefirst, second and third wavelengths λ1, λ2 and λ3;

wherein light sources to emit at least two light fluxes entering withrespective different magnifications into the objective optical systemamong the first, second and third light sources are packaged in a lightsource module and the divergent angle converting element is located on aoptical path between the light source module and the objective opticalsystem.

(8) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1for conducting recording and/or reproducing information for a firstinformation recording medium equipped with a protective substrate havinga thickness t1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1) for conducting recording and/or reproducing information for asecond information recording medium equipped with a protective substratehaving a thickness t2 (t2≧t1);

a third light source to emit a light flux having a third wavelength λ3(λ3>λ2>λ1) for conducting recording and/or reproducing information for athird information recording medium equipped with a protective substratehaving a thickness t3 (t3≧t2);

a diffractive lens having an optical surface including a superpositiontype diffractive structure,

wherein the superposition type diffractive structure includes aplurality of ring-shaped zones which are formed concentrically around anoptical axis, wherein each ring-shaped zone is composed of a pluralityof stepped section stepwise, wherein the superposition type diffractivestructure has a function to provide substantially no optical pathdifference to the first and third light fluxes and to provide an opticalpath difference only to the second light flux; and

a light converging element to converge a light flux having thewavelength λ1, λ2 or λ3 having passed through the diffractive lens ontothe first, second or third information recording medium respectively;

wherein the following formula (173) is satisfied:

m1≧m2>m3  (173)

where m1 is a magnification of an optical system structured by thediffractive lens and the light converging element for a light fluxhaving the first wavelength λ1, m2 is a magnification of an opticalsystem structured by the optical member and the light converging elementfor a light flux having the second wavelength λ2 and m3 is amagnification for a light flux having the third wavelength λ3.(9) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1for conducting recording and/or reproducing information for a firstinformation recording medium equipped with a protective substrate havinga thickness t1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1) for conducting recording and/or reproducing information for asecond information recording medium equipped with a protective substratehaving a thickness t2 (t2≧t1);

a third light source to emit a light flux having a third wavelength λ3(λ3>λ2>λ1) for conducting recording and/or reproducing information for athird information recording medium equipped with a protective substratehaving a thickness t3 (t3≧t2);

a light converging element to converge a light flux having thewavelength λ1, λ2 or λ3 onto the first, second or third informationrecording medium respectively;

a correcting optical system having an optical surface including apredetermined stepped structure; and

a spherical aberration correcting member;

wherein the correcting optical system has a function to correct aspherical aberration generated by the light converging element due to adifference between the first wavelength λ1 and the second wavelength λ2and/or a spherical aberration caused due to a difference between t1 andt2 and the spherical aberration correcting member has a function tocorrect a spherical aberration caused due to a difference between t1 andt3.

(10) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1);

an objective optical system for converging a light flux having the firstwavelength λ1 onto a recording plane of a first information recordingmedium equipped with a protective substrate having a thickness t1 andfor converging a light flux having the second wavelength λ2 onto arecording plane of a second information recording medium equipped with aprotective substrate having a thickness t2 (t2≧t1);

wherein the objective optical system comprises a first optical surfaceto provide substantially no optical path difference for an incidentlight flux having the first wavelength λ1 and to provide an optical pathdifference for an incident light flux having the second wavelength λ2and a second optical surface to refrain a chromatic aberration changecaused due to wavelength dispersion when the first wavelength λ1fluctuates within a range of ±10 nm.

(11) An optical pickup apparatus for conducting recording and/orreproducing information for plural different recording mediums withplural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ1;

a second light source to emit a light flux having a second wavelength λ2(λ2>λ1);

an objective optical system for converging a light flux having the firstwavelength λ1 onto a recording plane of a first information recordingmedium equipped with a protective substrate having a thickness t1 andfor converging a light flux having the second wavelength λ2 onto arecording plane of a second information recording medium equipped with aprotective substrate having a thickness t2 (t2≧t1);

wherein the objective optical system comprises a plastic lens having apositive paraxial power, a first optical surface to providesubstantially no optical path difference for an incident light fluxhaving the first wavelength λ1 and to provide an optical path differencefor an incident light flux having the second wavelength λ2, and a secondoptical surface to refrain a change of a spherical aberration caused dueto a change of a refractive index of the plastic lens when environmentaltemperature changes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a main portion showing a structure of anoptical pickup device.

FIGS. 2( a) to 2(c) each is a view showing a structure of asuperposition type diffraction optical element.

FIG. 3 is a plan view of a main portion showing a structure of anoptical pickup device.

FIGS. 4( a) to 4(c) each is a view showing a structure of asuperposition type diffraction optical element.

FIG. 5 is a plan view of a main portion showing a structure of anoptical pickup device.

FIGS. 6( a) to 6(c) each is a view showing a structure of asuperposition type diffraction optical element.

FIG. 7 is a plan view of a main portion showing a structure of anoptical pickup device.

FIGS. 8( a) and 8(b) each is a view showing a structure of asuperposition type diffraction optical element.

FIG. 9 is a view for explaining a principle of an action of asuperposition type diffractive structure.

FIG. 10 is a view for explaining a principle of an action of asuperposition type diffractive structure.

FIG. 11 is a view for explaining a principle of an action of asuperposition type diffractive structure.

FIG. 12 is a graph showing a relationship between the transmissionfactor of a wavelength selection filter and a numerical aperture.

FIG. 13 is a graph showing a relationship between the transmissionfactor of a wavelength selection filter and a numerical aperture.

FIG. 14 is a plan view of a main portion showing a structure of anoptical pickup device.

FIGS. 15( a) to 15(c) each is a view showing a structure of asuperposition type diffraction optical element.

FIG. 16 is a sectional view showing a structure of a superposition typediffraction optical element.

FIG. 17 is a sectional view showing a structure of a superposition typediffraction optical element.

FIG. 18 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 19 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 20 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 21 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 22 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 23 is an optical path view of an optical pickup device.

FIG. 24 is an optical path view of an optical pickup device.

FIG. 25 is an optical path view of an optical pickup device.

FIG. 26 is a view for explaining a superposition type diffractivestructure.

FIGS. 27( a) and 27(b) each is a view for explaining a diffractivestructure.

FIG. 28 is a view for explaining an optical path difference grantstructure.

FIG. 29 is a view for explaining a function of the optical pathdifference grant structure.

FIG. 30 is a plan view of a main portion showing a structure of anoptical pickup device.

FIG. 31 is a plan view of a main portion showing a structure of anoptical pickup device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the present specification, as a light source for therecording/reproducing, the optical disk for which the blue violetsemiconductor laser or blue violet SHG laser is used, is generallycalled as “high density optical disk”, and the recording/reproducing ofthe information by the objective optical system of NA 0.85 is conducted,and the recording/reproducing of the information by the objectiveoptical system of NA 0.65 is conducted other than the optical disk ofthe standard whose protective layer thickness is about 0.1 mm, and theoptical disk of the standard whose protective layer thickness is about0.6 mm, is also included. Further, other than the optical disk havingsuch a protective layer on its information recording surface, theoptical disk having the protective layer whose thickness is aboutseveral-several tens nm, on its information recording surface, or theoptical disk whose protective layer thickness, or protective filmthickness is 0, is also included. Further, in the present specification,in the high density optical disk, the optical magnetic disk which usesthe blue violet semiconductor laser or blue violet SHG laser as thelight source for the recording/reproducing of the information, is alsoincluded.

In the present specification, DVD is a general term of the optical diskof DVD series such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R,DVD-RW, DVD+R, and DVD+RW, and CD is a general term of the optical diskof CD series such as CD-ROM, CD-Audio, CD-Video, CD-R, and CD-RW.

“Optical system” in the present specification means an optical systemwhich emits a light flux emitted from a light source, has apredetermined optical function and is composed of one optical element orplural optical elements. “Objective optical system” and “correctingoptical system” mentioned later on are one example of it.

“Superposition type diffractive structure” indicates, as typically shownin FIG. 26, in a plurality of ring-shaped zones R3 i which arecontinuously arranged around the optical axis, a structure in which eachof ring-shaped zones R3 i is further divided stepwise by a plurality ofstepped sections d3 i in the optical axis direction. When the depth Δ ofthe stepped section d3 i and the number of stepped section N of such asuperposition type diffractive structure are adequately set, asdescribed above, an action by which only one of a plurality of lightfluxes whose wavelengths are different, is selectively diffracted, andthe light fluxes having the other wavelength are not diffracted andtransmitted as they are, or the diffraction orders of the light fluxesof a plurality of wavelengths are made different each other, or for thelight flux of specific wavelength, the diffraction efficiency isextremely reduced, can be given to a plurality of incident light fluxeswhose wavelengths are different. Hereupon, such an action by which thediffraction action or diffraction efficiency is extremely reduced, isgiven to the diffracted light ray having the maximum diffractionefficiency in the diffracted light ray of various degrees generated fromthe light fluxes of respective wavelengths. Hereupon, in the presentspecification, the light flux which is not diffracted by this“superposition type diffractive structure” (that is, the actual opticalpath difference is not given), but transmitted as it is, is called“0-degree diffracted light ray” for convenience.

In the present specification, the “diffractive structure” indicates, astypically shown in FIG. 27, a structure which is structured by aplurality of ring-shaped zones R1 i of saw-toothed shape (FIG. 27( a))or step shape (FIG. 27( b)), which is continuously arranged around theoptical axis, and each of ring-shaped zones R1 i is divided by thestepped section d1 i in the optical axis direction. This “diffractivestructure” generates the diffracted light ray of diffraction order whoseabsolute value is not smaller than 1. In the present specification, theabove-described “superposition type diffractive structure” in which eachring-shaped zone is further divided stepwise, is distinguished from this“diffractive structure”. Further, although FIG. 27 shows the case thatthe directions of the stepped sections d1 i are the same in theeffective diameter, “diffractive structure” of the present inventionincludes the case that the directions of the stepped sections d1 i areinverted in the effective diameter.

In the present specification, an “optical path difference grantstructure” indicates, as typically shown in FIG. 28, a structurestructured by a plurality of ring-shaped zones R2 i which arecontinuously arranged around the optical axis and divided by the steppedsection d2 i of the optical axis direction. That is, it means a steppedstructure in which a plurality of ring-shaped zones are formedcontinuously around the optical axis as the center are divided with astepped section so as to provide a predetermined optical pathdifference. In these ring-shaped zones R2 i, the ring-shaped zone of theinner side than the ring-shaped zone positioned at a predeterminedheight within the maximum effective diameter is shifted in the opticalaxis direction in such a manner that the optical path length is reducedas it is separated from the optical axis, and the ring-shaped zone ofthe outer side than the ring-shaped zone positioned at a predeterminedheight within the maximum effective diameter is shifted in such a mannerthat the optical path length is increased as it is separated from theoptical axis. As the ring-shaped zone positioned at a predeterminedheight called herein, it is preferable that the height from the opticalaxis in its central portion is the height within the range of 60% to 85%of the maximum effective diameter.

Further, in the present specification, the “optical path differencegrant structure” can also be expressed as a structure which isstructured by a plurality of ring-shaped zones R2 i divided by minutestepped section d2 i in the central area C including the optical axisand outside the central area C, and in which the ring-shaped zone R2 iAadjoining the outside of the central area C is formed by shifting in theoptical axis direction so that the optical axis length is more increasedthan the ring-shaped zone R2 iC adjoining its inside, and onering-shaped zone R2 iD whose central portion is positioned at the heightwithin the range of 60% to 85% of the maximum effective diameter isformed by shifting in the optical axis so that the optical path lengthis more reduced than the ring-shaped zone 21E adjoining its inside andthe ring-shaped zone 21F adjoining its outside. The “central area C”called herein, is an optical function area which is surrounded by thestepped section d2 iA which includes the optical axis and is positionedat the nearest position from the optical axis.

It becomes possible that the spherical aberration is corrected by theoptical path difference grant structure structured in this manner. Forexample, in the objective optical system structured by the aberrationcorrecting element and light converging element both of which are formedof plastic lenses, when the spherical aberration change accompanied bythe temperature increase (refer to the wave-front aberration a in FIG.29) is corrected by the aberration correcting element by which theoptical path difference grant structure is formed, the depth of thestepped section d2 i is set so as to satisfy d2 i=p·λ0/(N0−1). Where, pis an integer not smaller than 1, λ0 (μm) is a designed wavelength, andN0 is the refractive index of the plastic lens at the design referencetemperature.

At the reference temperature, because the optical path difference by thestepped section d2 i is integer times of designed wavelength,practically the optical path difference is not given. In contrast tothis, when the temperature is risen, because the refractive index of theplastic lens is decreased, the optical path difference by the steppedsection d2 i is minutely shifted from the integer times of the designedwavelength, as shown by b in FIG. 29, and the wave-front aberration ofreversal sign to the wave-front aberration (a in FIG. 29) of the lightconverging element when the temperature rises, is generated, andrespective wave-front aberrations act in the direction of cancelled-out(c in FIG. 29).

Hereupon, FIG. 26 to FIG. 28 are outline views when each structure isformed on parallel plane plate, and in the present specification, eachstructure is not limited to only the shape of FIG. 26 to FIG. 28, as faras it does not depart from the above-described definition.

In the present specification, the “aberration correcting element”indicates an optical element on whose optical surface theabove-described superposition type diffractive structure is formed, andwhich has a function to suppress the spherical aberration generated dueto the difference of the protective layer thickness between a pluralityof optical disks whose protective layer thickness is different. Further,in the present specification, the aberration correcting element is notonly one optical element, but it may also be a structure formed of aplurality of optical elements. Further, the “light converging element”indicates an optical element which is arranged in the position facingthe optical disk in the optical pickup device, and which has a functionby which the light flux projected from the aberration correcting elementis light-converged, and image-focused on respective informationrecording surfaces of a plurality of kinds of optical disks whosestandards are different. Also this “light converging element” is notonly one optical element, but may also be a structure formed of aplurality of optical elements. And herein, as the aberration correctingelement like this, “aberration correcting element” means an opticalsystem composed of one optical element or plural optical elements so asto correct an optical aberration caused by various factors.

In the present specification, the “objective optical system” indicatesan optical system including at least the above-described lightconverging element. The objective optical system may also be structuredby only the light converging element.

Further, in the present specification, when there is an optical elementwhich conducts the tracking and focusing by the actuator by beingintegrated with such a light converging element, the optical systemstructured by these optical element and light converging element isdefined as the objective optical system. Accordingly, in the opticalelement which is integrated with the light converging element and whichconducts tracking and focusing by the actuator, the above-describedaberration correcting element is included.

In the present specification, a phrase of “fine wave-front is formed” onthe information recording surface of the optical disk is the samemeaning as a case in which the incident light flux is light-converged onthe information recording surface so that the wave-front aberration isin the situation not larger than 0.07λ RMS.

In order to solve the problems as described above, the invention writtenin item 1 is an optical element for an optical pickup device by which,by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the first optical information recording medium havingthe protective layer of thickness t1, and by using the light flux of thesecond wavelength λ2 (λ2>λ1) projected from the second light source, thereproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1), and characterized in that: the optical elementhas an optical function surface on which the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones in which a plurality of stepped section are formed,are arranged around the optical axis, is formed; and an optical functionsurface on which the diffractive structure structured by a plurality ofring-shaped zones which are divided by the stepped section of theoptical axis direction is formed.

The invention written in item 2 is characterized in that: in the opticalelement for the optical pickup device written in item 1, when thediffraction order of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the first wavelength λ1 enters into the diffractivestructure is n1, and the diffraction order of the diffracted light rayhaving the maximum diffraction efficiency in the diffracted light raygenerated when the light flux of the second wavelength λ2 enters intothe diffractive structure is n2, the depth of stepped section of thediffractive structure is set so as to satisfy the following expression(1).

n1>n2  (1)

The invention written in item 3 is characterized in that: in the opticalelement for the optical pickup device written in item 1 or 2, the firstwavelength λ1 (μm), the second wavelength λ2 (μm) respectively satisfythe following expressions (2) and (3), and a combination of thediffraction order n1 of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the first wavelength λ1 enters into the diffractivestructure, and the diffraction order n2 of the diffracted light rayhaving the maximum diffraction efficiency in the diffracted light raygenerated when the light flux of the second wavelength λ2 enters intothe diffractive structure, is any one of (n1, n2)=(2, 1), (3, 2), (5,3), (8, 5), (10, 6).

0.39<λ1<0.42  (2)

0.63<λ2<0.68  (3)

The invention written in item 4 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to3, the element having the optical function surface on which diffractivestructure is formed, in the optical elements, is formed of the materialin which its refractive index in the first wavelength λ1 is within therange of 1.5-1.6, and Abbe's number on the d line is within the range of50-60, and the depth d1 in the optical axis direction of the steppedsection closest to the optical axis in the stepped section of thediffractive structure, satisfies any one of the following expressions(4) to (8).

1. 2 μm<d1<1.7 μm  (4)

2. 0 μm<d1<2.6 μm  (5)

3. 4 μm<d1<4.1 μm  (6)

5. 6 μm<d1<6.5 μm  (7)

6. 9 μm<d1<8.1 μm  (8)

The invention written in item 5 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to4, the sectional shape including the optical axis of the diffractivestructure is a step shape.

The invention written in item 6 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to4, the sectional shape including the optical axis of the diffractivestructure is a saw-toothed shape.

The invention written in item 7 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to6, the optical element is formed of one element, and the superpositiontype diffractive structure is formed on one optical function surface ofthe optical element, and the diffractive structure is formed on theother optical function surface of the optical element.

The invention written in item 8 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to7, the superposition type diffractive structure does not actually givethe optical path difference between adjoining ring-shaped zones to thelight flux of the first wavelength λ1, but gives the optical pathdifference to the light flux of the second wavelength λ2.

The invention written in item 9 is characterized in that: in the opticalelement for the optical pickup device written in any one of items 1 to8, the first wavelength λ1 (μm), the second wavelength λ2 (μm)respectively satisfy the following expressions (2) and (3).

0.39<λ1<0.42  (2)

0.63<λ2<0.68  (3)

The invention written in item 10 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, and the reproducing and/or recording of theinformation is conducted for the second optical information recordingmedium having the protective layer of thickness t2 (t2≧t1) by using thelight flux of the second wavelength λ2 (λ2>λ1) projected from the secondlight source, and the optical element has; an optical function surfaceon which the superposition type diffractive structure which is astructure in which a plurality of ring-shaped zones in which a pluralityof stepped section are formed, are arranged around the optical axis, isformed; and an optical function surface on which the optical path grantstructure, structured by a plurality of ring-shaped zones divided bystepped section in the optical axis direction, is formed.

The invention written in item 11 is characterized in that: in theoptical element for the optical pickup device written in item 10, in thering-shaped zones of the optical path grant structure, the ring-shapedzone of inner side than the ring-shaped zone positioned at apredetermined height in the maximum effective diameter is shifted in theoptical axis direction so that the optical path is more reduced as it isseparated from the optical axis, and the ring-shaped zone of outer sidethan the ring-shaped zone positioned at a predetermined height in themaximum effective diameter is shifted in the optical axis direction sothat the optical path is more increased as it is separated from theoptical axis.

The invention written in item 12 is characterized in that: in theoptical element for the optical pickup device written in item 11, theheight from the optical axis in the central portion of the ring-shapedzone positioned at the predetermined height is a height within the rangeof 60% to 85% of the maximum effective diameter.

The invention written in item 13 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 10 to 12, Φ1, Φ2 respectively expressed by following expressions(9) and (10), by the first wavelength λ1 (μm), second wavelength λ2(μm), the depth d2 (μm) in the optical axis direction of the steppedsection nearest the optical axis in the stepped sections of the opticalpath difference grant structure, refractive index Nλ1 to the firstwavelength λ1 of the element having the optical function surface onwhich the optical path difference grant structure is formed, in theoptical elements, and refractive index Nλ2 to the second wavelength λ2of the optical element, satisfy the following expressions (11) to (13).

Φ1=d2(Nλ1−1)/λ1  (9)

Φ2=d2(Nλ2−1)/λ2  (10)

INT(Φ1)≦20  (11)

0≦|INT(Φ1)−Φ1|≦0.4  (12)

0≦|INT(Φ2)−Φ2|≦0.4  (13)

Where, INT (Φ(i) (i=1, 2) is an integer obtained by half-adjusting Φi.

The invention written in item 14 is characterized in that: in theoptical element for the optical pickup device written in item 13, in theoptical elements, the element having the optical function surface onwhich the optical difference grant structure is formed, is formed of amaterial in which the refractive index in the first wavelength λ1 iswithin the range of 1.5-1.6, and Abbe's number on d line is within therange of 50-60, and satisfies the following expressions (14) and (15).

INT(Φ1)=5p  (14)

INT(Φ2)=3p  (15)

Where, p is an integer not smaller than 1.

The invention written in item 15 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 10-14, the optical element is structured by one element, and thesuperposition type diffractive structure is formed on one opticalfunction surface of the optical element, and the optical path differencegrant structure is formed on the other optical function surface of theoptical element.

The invention written in item 16 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 10-15, the superposition type diffractive structure does notpractically give the optical path difference between adjoiningring-shaped zones to the light flux of the first wavelength λ1, butgives the optical path difference to the light flux of the secondwavelength λ2.

The invention written in item 17 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 10-16, the first wavelength λ1 (μm), second wavelength λ2 (μm)respectively satisfy the following expressions (2) and (3).

0.39<λ1<0.42  (2)

0.63<λ2<0.68  (3)

The invention written in item 18 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 1-17, the first wavelength λ1 (μm), second wavelength λ2 (μm)satisfy the following expressions (2) and (3), and in the superpositiontype diffractive structure, the depth Δ(μm) in the optical axisdirection of the stepped section formed in each ring-shaped zone, and inthe optical elements, refractive index Nλ1 to the first wavelength λ1 ofthe element having the optical function surface on which thesuperposition type diffractive structure is formed, practically satisfythe following expression (16).

0.39<λ1<0.42  (2)

0.63<λ2<0.68  (3)

Δ=2m·λ1/(Nλ1−1)  (16)

Where, N is any one of 3 or 4, or 5, and m is an integer not smallerthan 1.

The invention written in item 19 is characterized in that: in theoptical element for the optical pickup device written in item 18, in theoptical elements, the element having the optical function surface onwhich the superposition type diffractive structure is formed, is formedof the material in which the refractive index in the first wavelength λ1is within the range of 1.5-1.6, and Abbe's number on d line is withinthe range of 50-60, and in the superposition type diffractive structure,a combination of the number N of the stepped sections formed in eachring-shaped zone and the depth D (μm) in the optical axis direction ofthe ring-shaped zone nearest the optical axis in the ring-shaped zones,is any one of the following expressions (17) to (19).

When N=3, 4.1≦D≦4.8  (17)

When N=4, 5.4≦D≦6.4  (18)

When N=5, 7.0≦D≦7.9  (19)

The invention written in item 20 is characterized in that: it is anobjective optical system which is used for the optical pickup device bywhich the reproducing and/or recording of the information is conductedfor the first optical information recording medium having the protectivelayer of the thickness t1 by using the light flux of the firstwavelength λ1 projected from the first light source, and the reproducingand/or recording of the information is conducted for the second opticalinformation recording medium having the protective layer of thethickness t2 (t2≧t1) by using the light flux of the second wavelength λ2(λ2>λ1) projected from the second light source, and is used for thepurpose in which the light flux of the first wavelength λ1 islight-converged on the information recording surface of the firstoptical information recording medium and the light flux of the secondwavelength λ2 is light-converged on the information recording surface ofthe second optical information recording medium; it includes the opticalelement for the optical pickup device written in any one of items 1 to9; and the diffractive structure has a function by which the chromaticaberration generated due to the wavelength dispersion of the objectiveoptical system is suppressed when the first wavelength λ1 is changedwithin the range of ±10 nm.

The invention written in item 21 is characterized in that: in theobjective optical system written in item 20, the diffractive structurehas a function by which the chromatic aberration on axis of theobjective optical system is suppressed when the first wavelength λ1 ischanged within the range of ±10 nm.

The invention written in item 22 is characterized in that: in theobjective optical system written in item 20 or 21, the diffractivestructure has a function by which the spherical aberration changegenerated due to the wavelength dispersion of the objective opticalsystem is suppressed when the first wavelength λ1 is changed within therange of ±10 nm.

The invention written in item 23 is characterized in that: it is anobjective optical system which is used for the optical pickup device bywhich the reproducing and/or recording of the information is conductedfor the first optical information recording medium having the protectivelayer of thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, and the reproducing and/orrecording of the information is conducted for the second opticalinformation recording medium having the protective layer of thickness t2(t2≧t1) by using the light flux of the second wavelength λ2 (λ2>λ1)projected from the second light source; and which is used for thepurpose by which the light flux of the first wavelength λ1 islight-converged on the information recording surface of the firstinformation recording medium, and the light flux of the secondwavelength λ2 is light-converged on the information recording surface ofthe second information recording medium; it includes the optical elementfor the optical pickup device written in any one of items 1 to 9; andthe objective optical system has a plastic lens whose paraxial power ispositive, and the diffractive structure has a function by which thespherical aberration change generated due to the refractive index changeof the plastic lens accompanied by the environmental temperature changeis suppressed.

The invention written in item 24 is characterized in that: in theobjective optical system written in item 23, the objective opticalsystem has the wavelength dependency of the spherical aberration bywhich, when the first wavelength λ1 is changed toward the longwavelength side, the spherical aberration is changed to under correctiondirection, and when the first wavelength λ1 is changed toward the shortwavelength side, the spherical aberration is changed to over correctiondirection.

The invention written in item 25 is characterized in that: in theobjective optical system written in any one of items 20-24, theobjective optical system is structured by an aberration correctingelement, and a light converging element used for a purpose by which thelight flux of the first wavelength λ1 projected from the aberrationcorrecting element is light-converged on the information recordingsurface of the first optical information recording medium, and the lightflux of the second wavelength λ2 projected from the aberrationcorrecting element is light-converged on the information recordingsurface of the second optical information recording medium, and thesuperposition type diffractive structure and the diffractive structureare formed on the optical function surface of the aberration correctingelement.

The invention written in item 26 is characterized in that: in theobjective optical system written in any one of items 20-25, thesectional shape including the optical axis of the diffractive structureis a step shape.

The invention written in item 27 is characterized in that: in theobjective optical system written in any one of items 20-27, thesectional shape including the optical axis of the diffractive structureis a saw-toothed shape.

The invention written in item 28 is characterized in that: in theobjective optical system written in any one of items 20-27, thesuperposition type diffractive structure has a function by which thespherical aberration generated due to the difference of the thicknessbetween the protective layer of the first optical information recordingmedium and the protective layer of the second optical informationmedium, is corrected.

The invention written in item 29 is characterized in that: an objectiveoptical system used for an optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, and the reproducing and/orrecording of the information is conducted for the second opticalinformation recording medium having the protective layer of thickness t2(t2≧t1) by using the light flux of the second wavelength λ2 (λ2>λ1)projected from the second light source, and used for a purpose by whichthe light flux of the first wavelength λ1 is light-converged on theinformation recording surface of the first optical information recordingmedium, and the light flux of the second wavelength λ2 islight-converged on the information recording surface of the secondoptical information recording medium; and it includes an optical elementfor the optical pickup device written in any one of items 10 to 17, andthe objective optical system has a plastic lens whose paraxial power ispositive, and the optical path grant structure has a function by whichthe spherical aberration change generated due to the wavelengthdispersion of the objective optical system is suppressed, when the firstwavelength λ1 is changed within the range of ±10 nm.

The invention written in item 30 is characterized in that: an objectiveoptical system used for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, and the reproducing and/orrecording of the information is conducted for the second opticalinformation recording medium having the protective layer of thickness t2(t2≧t1) by using the light flux of the second wavelength λ2 (λ2>λ1)projected from the second light source, and used for a purpose by whichthe light flux of the first wavelength λ1 is light-converged on theinformation recording surface of the first optical information recordingmedium, and the light flux of the second wavelength λ2 islight-converged on the information recording surface of the secondoptical information recording medium; and it includes an optical elementfor the optical pickup device written in any one of items 10 to 17, andthe objective optical system has a plastic lens whose paraxial power ispositive, and the optical path grant structure has a function by whichthe spherical aberration change generated due to the refractive indexchange of the plastic lens accompanied by the environmental temperaturechange is suppressed.

The invention written in item 31 is characterized in that: in theobjective optical system written in item 30, the optical path grantstructure has the temperature dependency of the spherical aberrationlike as that, when the environmental temperature rises, the sphericalaberration added to the light flux of the first wavelength λ1 is changedtoward the under correction direction, and when the environmentaltemperature lowers, the spherical aberration added to the light flux ofthe first wavelength λ1 is changed toward the under correctiondirection.

The invention written in item 32 is characterized in that: in theobjective optical system written in item 30 or 31, in the ring-shapedzone of the optical path difference grant structure, the ring-shapedzone of the inner side than the ring-shaped zone positioned at apredetermined height in the maximum effective diameter is shifted in theoptical axis direction in such a manner that the optical path is reducedas it is separated from the optical axis, and the ring-shaped zone ofthe outer side than the ring-shaped zone positioned at a predeterminedheight in the maximum effective diameter is shifted in the optical axisdirection in such a manner that the optical path is increased as it isseparated from the optical axis.

The invention written in item 33 is characterized in that: in theobjective optical system written in item 32, the height from the opticalaxis at the central portion of the ring-shaped zone positioned at apredetermined height is the height within the range of 60% to 85% of themaximum effective diameter.

The invention written in item 34 is characterized in that: in theobjective optical system written in any one of items 29 to 33, theobjective optical system is structured by an aberration correctingelement, and a light converging element used for a purpose by which thelight flux of the first wavelength λ1 projected from the aberrationcorrecting element is light-converged on the information recordingsurface of the first optical information recording medium, and the lightflux of the second wavelength λ2 projected from the aberrationcorrecting element is light-converged on the information recordingsurface of the second optical information recording medium, and thesuperposition type diffractive structure and the optical path differencegrant structure are formed on the optical function surface of theaberration correcting element.

The invention written in item 35 is characterized in that: in theobjective optical system written in any one of items 29 to 34, thesuperposition type diffractive structure has a function by which thespherical aberration generated due to the difference of the thicknessbetween the protective layer of the first optical information recordingmedium and the protective layer of the second optical informationrecording medium is corrected.

The invention written in item 36 is characterized in that: in theobjective optical system written in any one of items 20 to 35, when theoptical path difference added to the transmission wave-front by thesuperposition type diffractive structure is defined by the followingarithmetic expression, signs of B₂ and B₄ are different each other.

$\begin{matrix}{\varphi_{b} = {{\lambda/\lambda_{B}} \times n \times {\sum\limits_{j = 1}\; {B_{2j}h^{2j}}}}} & \lbrack {{Arith}.\mspace{14mu} 1} \rbrack\end{matrix}$

Where, λ is a wavelength of the incident light flux, λ_(B) is aproduction wavelength, h is the height (mm) in the directionperpendicular to the optical axis, B_(2j) is a optical path differencefunction coefficient, and n is the diffraction order.

The invention written in item 37 is characterized in that: in theobjective optical system written in any one of items 20 to 36, theobjective optical system is structured by an aberration correctingelement having the optical function surface on which the superpositiontype diffractive structure is formed; and a light converging elementwhich is a plastic lens of 1 group 1 lens composition used for a purposeby which the light flux of the first wavelength λ1 projected from theaberration correcting element, is light-converged on the informationrecording surface of the first optical information recording medium, andthe light flux of the second wavelength λ2 projected from the aberrationcorrecting element, is light-converged on the information recordingsurface of the second optical information recording medium; and theparaxial power P1 (mm⁻¹) of the aberration correcting element for thefirst wavelength λ1 satisfies the following expression (20).

P1>0  (20)

The invention written in item 38 is characterized in that: in theobjective optical system written in any one of items 20 to 37, theobjective optical system is structured by an aberration correctingelement having the optical function surface on which the superpositiontype diffractive structure is formed; and a light converging element of1 group 1 lens composition used for a purpose by which the light flux ofthe first wavelength λ1 projected from the aberration correctingelement, is light-converged on the information recording surface of thefirst optical information recording medium, and the light flux of thesecond wavelength λ2 projected from the aberration correcting element,is light-converged on the information recording surface of the secondoptical information recording medium; and a ratio of the paraxial powerP1 (mm⁻¹) of the aberration correcting element for the first wavelengthλ1 and the paraxial power P2 (mm⁻¹) of the light converging element forthe first wavelength λ1 satisfies the following expression (21).

|P1/P2|≦0.2  (21)

The invention written in item 39 is characterized in that: in theobjective optical system written in item 38, the light convergingelement is a ring poly-olefin series plastic lens, and in the plasticlens, the refractive index N405 to the wavelength 405 nm at temperature25° C., and Abbe's number νd in d line, the change ratio dN405/dT of therefractive index to the wavelength 405 nm accompanied by the temperaturechange within the temperature range of −5° C.-70° C., satisfy thefollowing expressions (22) to (24).

1.54<N405<1.58  (22)

50<νd<60  (23)

−10×10⁻⁵ (° C.⁻¹)<dN405/dT<−8×10⁻⁵ (° C.⁻¹)  (24)

The invention written in item 40 is characterized in that: in theobjective optical system written in item 38, the light convergingelement is molded by using the material in which particles whosediameter is not larger than 30 μm, are dispersed in plastic materials.

The invention written in item 41 is characterized in that: in theobjective optical system written in item 38, the light convergingelement is a glass lens.

The invention written in item 42 is characterized in that: an opticalpickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,and the reproducing and/or recording of the information is conducted forthe second optical information recording medium having the protectivelayer of thickness t2 (t2≧t1) by using the light flux of the secondwavelength λ2 (λ2>λ1) projected from the second light source, and it hasan optical element for the optical pickup device written in any one ofitems 1 to 19.

The invention written in item 43 is characterized in that: an opticalpickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,and the reproducing and/or recording of the information is conducted forthe second optical information recording medium having the protectivelayer of thickness t2 (t2≧t1) by using the light flux of thesecond-wavelength λ2 (λ2>λ1) projected from the second light source, andit has an objective optical system written in any one of items 20 to 41.

The invention written in item 44 is characterized in that: it is anoptical information recording reproducing device in which the opticalpickup device written in item 42 or 43 is mounted, and which can conductat least one of the following (I) to (IV).

-   (I) the recording of the information for the first optical    information recording medium, and the recording of the information    for the second optical information recording medium-   (II) the recording of the information for the first optical    information recording medium, and the reproducing of the information    recorded in the second optical information recording medium-   (III) the reproducing of the information recorded in the first    optical information recording medium, and the recording of the    information for the second optical information recording medium-   (IV) the reproducing of the information recorded in the first    optical information recording medium, and the reproducing of the    information recorded in the second optical information recording    medium

According to the invention written in item 1, when the number of steppedsections formed in each ring-shaped zone of the superposition typediffractive structure, the depth of the stepped section formed in eachring-shaped zone, and the arrangement of each ring-shaped zone areadequately set, because, to the light flux of the first wavelength λ1,the optical path difference is not practically given, and the light fluxis not diffracted and passed as it is, and to the light flux of thesecond wavelength λ2, the optical path difference is given, and thelight flux can be diffracted, the spherical aberration generated due tothe difference of the protective layer thickness between the highdensity optical disk and DVD can be corrected, and the high transmissionfactor (diffraction efficiency) can be secured also to the light flux ofany wavelength. Further, on the superposition type diffractivestructure, a role of a dichroic filter by which the light flux of thefirst wavelength λ1 is not diffracted, and transmitted as it is, and tothe light flux of the second wavelength λ2, the diffraction efficiencyis extremely reduced, and the light flux is made flare, can also becharged.

For example, in the common objective optical system of the high densityoptical disk and DVD, when, in numerical aperture NA2 of DVD, the firstsuperposition type diffractive structure for correcting the sphericalaberration generated due to the difference of the protective layerthickness between the high density optical disk and DVD is formed, andfurther, in the range from numerical aperture NA2 to numerical apertureNA1 of the high density optical disk, the second superposition typediffractive structure by which the light flux of the first wavelength λ1is not diffracted and passed as it is, and to the light flux of thesecond wavelength λ2, the diffraction efficiency is extremely reducedand the light flux is made flare, is formed, the objective opticalsystem by which the recording/reproducing of the information can beadequately conducted for any optical disk, and which has an apertureswitching function for DVD can be provided.

Further, in order to enable the recording/reproducing of the informationto be conducted adequately for the high density optical disk, byproviding a means for correcting the chromatic aberration on the axis,it is necessary to prevent the deterioration of the light convergingperformance due to the instantaneous wavelength change of the laserlight source, which is called mode-hopping. This is for the reason that,because the wavelength dispersion of the optical material in the blueviolet area is very increased, the dislocation of the focus position islargely generated for even a slight wavelength change.

Further, as one standard of the high density optical disk, an opticaldisk in which the numeral aperture of the objective optical system isincreased to about 0.85, is proposed, however, as the numerical apertureof the objective optical system is increased, because the sphericalaberration change generated by the wavelength change of the incidentlight flux is increased, a problem that the laser light source havingthe wavelength error by the production error can not be used, isactualized. Therefore, because it is necessary that laser light sourcesare selected, the production cost of the optical pickup device isincreased.

Further, because the specific gravity of plastic lens is smaller thanthat of glass lens, the burden on the actuator to drive the objectiveoptical system can be reduced, and the following of the objectiveoptical system can be conducted at high speed. Further, the plastic lensproduced by the injection molding can be mass-produced high accuratelyat the stable quality, when a desired metallic mold is accuratelyproduced. However, in the case where the numerical aperture of theobjective optical system is increased, when the objective optical systemis formed of the plastic lens, the influence of the refractive indexchange following the temperature change is increased. This is for thereason that the spherical aberration generated by the refractive indexchange is increased in proportion to fourth power of the numericalaperture.

Accordingly, in the present invention, when the diffractive structure isprovided on the optical function surface of the optical element, becausea function to suppress the dislocation of the focus position to thewavelength change of the incident light flux, or the sphericalaberration change to the wavelength change of the incident light flux,or the spherical aberration change following the refractive indexchange, is added, even when the wavelength change of the incident lightflux or temperature change is generated, the recording/reproducingcharacteristic to the high density optical disk can be finelymaintained.

However, because, in the light source for the high density optical diskand the light source for DVD, the wavelength difference is large, whenthe diffracted light ray of the same diffraction order generated in theabove-described diffractive structure is used as the light flux for therecording/reproducing for respective optical disks, the diffractionefficiency sufficient for the light fluxes of the wavelength of 2 lightsources, can not be obtained. For such a problem, as in the invention ofitem 2, when the diffractive structure is designed in such a manner thatthe diffraction order n2 of the diffracted light ray used for DVD islower degree than the diffraction order n1 of the diffracted light rayused for the high density optical disk, the diffraction efficiency forthe light fluxes of the wavelength of 2 light sources can besufficiently secured.

Specifically, as the diffraction orders n1, n2, when they have acombination as in the invention of item 3, it is preferable because thehigh diffraction efficiency can be secured for the wavelength of thewavelength λ1, λ2. There is a combination of the diffraction orders n1,n2 by which the high diffraction efficiency can be secured also for thelight flux having any wavelength, except the combination written in item3, however, when the diffraction order is too increased, because thelowering of the diffraction efficiency following the wavelength changeof the incident light flux becomes large, it is not preferable.

In the case where the element on which the diffractive structure isformed, is formed of the material in which the refractive index to thefirst wavelength λ1 is within the range of 1.5-1.6, and Abbe's number ond-line is within the range of 50-60, as written in the invention of item4, when, in the stepped section of the diffractive structure, the depthd1 of the stepped section at a position closest to the optical axis isset so as to satisfy any one of expressions (4)-(8), thehigh-diffraction efficiency can be secured for the light fluxes of thefirst wavelength λ1 and the second wavelength λ2. Hereupon, acombination of the diffraction orders n1, n2 and the stepped section d1has a relationship in which (n1, n2)=(2, 1) corresponds to expression(4), (n1, n2)=(3, 2) corresponds to expression (5), (n1, n2)=(5, 3)corresponds to expression (6), (n1, n2)=(8, 5) corresponds to expression(7), and (n1, n2)=(10, 6) corresponds to expression (8).

As the specific shape of such a diffractive structure, as in theinvention written in item 5, the shape in which the sectional shapeincluding the optical axis is step shape, is listed. Further, as thespecific shape of such a diffractive structure, as in the inventionwritten in item 6, the shape in which the sectional shape including theoptical axis may also be saw-toothed shape.

In order to give the high added value to the optical element andsimultaneously to attain the cost reduction, as written in the inventionof item 7, it is preferable that the optical element is formed of oneelement, and the superposition type diffractive structure and thediffractive structure are formed on respective optical function surfacesof the element.

As described above, because the wavelength dispersion is increased bymaking the light source wavelength short, in the objective opticalsystem, a problem of the chromatic aberration is actualized. The“chromatic aberration” said herein, indicates at least one of the“chromatic aberration on axis” in which the paraxial focusing positionis moved by the wavelength change, and the “chromatic sphericalaberration” in which the spherical aberration is changed by thewavelength change. Particularly, because the spherical aberration isincreased in proportion to the fourth power of the numerical aperture,when the objective optical system is made to increase the numericalaperture, the problem of the above-described “chromatic sphericalaberration” is more actualized. Accordingly, as in the inventions ofitems 20 to 22, in order to make enable to adequately conduct therecording/reproducing of the information for the high density opticaldisk, it is preferable to give a function by which the chromaticaberration generated due to the wavelength dispersion of the objectiveoptical system is suppressed, to the diffractive structure. Further, itis advantageous for the cost reduction and weight reduction that theobjective optical system is structured by plastic lens, however, becausethe influence of the refractive index change following the temperaturechange becomes large, when the temperature in the optical pickup deviceis changed, the recording/reproducing characteristic of the informationfor the high density optical disk is interfered. In order to maintainthe fine recording/reproducing characteristic even when the temperaturein the optical pickup device is changed, as in the invention of item 23,it is preferable to give a function by which the spherical aberrationgenerated due to the refractive index change of the plastic lens issuppressed, to the diffractive structure.

Specifically, as in the invention of item 24, it is preferable that thewavelength dependency of the spherical aberration in such a manner that,when the first wavelength λ1 is increased, the spherical aberration ischanged to under correction direction, and when the first wavelength λ1is reduced, the spherical aberration is changed to over correctiondirection, is given to the objective optical system by the action of thediffractive structure.

Further, when the structure having the stepped section of the opticalaxis direction such as the superposition type diffractive structure ordiffractive structure, is formed on the optical element whose curvatureis large, the transmission factor is lowered by the influence of shadingof the light flux by the stepped section portion. In order to preventsuch a lowering of transmission factor, as in the invention written initem 25, it is preferable that the objective optical system isstructured by the aberration correcting element and the light convergingelement, and the superposition type diffractive structure anddiffractive structure are formed on the aberration correcting element.

According to the invention written in item 10, as the same as theinvention written in item 1, by the superposition type diffractivestructure, the spherical aberration generated due to the difference ofthe protective layer thickness between the high density optical disk andDVD can be corrected, and the high transmission factor (diffractionefficiency) can be secured also for the light flux of any wavelength.Further, on the superposition type diffractive structure, a role of adichroic filter by which the light flux of the first wavelength λ1passes as it is without being diffracted, and for the light flux of thesecond wavelength λ2, the diffraction efficiency is extremely reducedand the light flux is made flare, can be burdened.

Further, in the present invention, when the optical path differencegrant structure is provided on an optical function surface of theoptical element, because a function to suppress the spherical aberrationchange to the wavelength change of the incident light flux, or thespherical aberration change following the refractive index change, isgiven to the optical function surface, even when the wavelength changeof the incident light flux or temperature change is caused, therecording/reproducing characteristic for the high density optical diskcan be finely maintained.

In order to correct the spherical aberration by the optical pathdifference grant structure, as in the invention of item 11, in thering-shaped zones of the optical path difference grant structure, astructure in which the ring-shaped zone of the inner side than thering-shaped zone positioned at a predetermined height within the maximumeffective diameter is shifted in the optical axis direction in such amanner that, as it is separated from the optical axis, the optical pathlength is shortened, is preferable, hereby, the spherical aberrationchange to the wavelength change of the incident light flux or thespherical aberration change following the refractive index change can besuppressed.

It is preferable that above-described height from the optical axis atthe central portion of the ring-shaped zone positioned at apredetermined height is, as in the invention of item 12, the heightwithin the range of 60% to 85% of the maximum effective diameter.

As in the invention of item 13, in order to increase the transmissionfactor of the optical path difference grant structure to the lightfluxes of the first wavelength λ1 and the second wavelength λ2, it ispreferable that, in the stepped section of the optical path differencegrant structure, the depth d2 of the stepped section positioned at theclosest position to the optical axis, and the optical path differencesΦ1 and Φ2 added to the light fluxes of the first wavelength λ1 and thesecond wavelength λ2 by the stepped section are set so that they satisfyexpressions (11) to (13). When these expressions are not satisfied, atthe time of the wavelength change of the incident light flux or at thetime of the refractive index change following the temperature change,the high degree of spherical aberration is generated to the light fluxof any wavelength. Although it is said that the high degree of sphericalaberration does not influence on the recording/reproducing performance,it is practically equivalence to the lowering of the transmissionfactor. When these expressions are satisfied, the generation of the highdegree of spherical aberration can be suppressed also to the light fluxof any wavelength, and the transmission factor can be increased.

When the element on which the optical path difference grant structure isformed is formed of the material in which the refractive index to thefirst wavelength λ1 is within the range of 1.5-1.6, and Abbe's number ond-line is within the range of 50-60, as in the invention of item 14, itis preferable that the optical path differences Φ1 and Φ2 satisfyexpressions (14) and (15). The expression (14) means that the opticalpath Φ1 added to the light flux of the first wavelength λ1 by thestepped section positioned at the position closest to the optical axisis about 5 times of the first wavelength λ1. When the depth d2 of thestepped section positioned at the position closes to the optical axis isset in this manner, because the optical path difference Φ2 added to thesecond wavelength λ2 is practically about 3 times of the secondwavelength λ2, the generation of the high degree of spherical aberrationcan be suppressed to the light flux of any wavelength, and thetransmission factor can be increased.

A specific example will be listed and explained below. In an opticalplastic material “ZEONEX 330R” (trade name) made by Nippon Zeon (co.),when the first wavelength λ1 and the second wavelength λ2 arerespectively 0.405 μm, and 0.655 μm, the refractive index Nλ1 to thefirst wavelength λ1 is 1.5252, and the refractive index Nλ2 to thesecond wavelength λ2 is 1.5070. When the depth d2 of the stepped sectionpositioned at a position closest to the optical axis is a depthdetermined by

d2=5·λ1/(Nλ1−1)=5·0.405/(1.5252−1)=3.856 μm.

the optical path difference Φ1 added to the light flux of the firstwavelength λ1 by this stepped section is 5 times of the first wavelengthλ1 (that is, p=1 in the expression (14)). The optical path difference Φ2added to the light flux of the first wavelength λ2 by this steppedsection of this depth is, from the expression (10),

Φ2=d2·(Nλ2−1)/λ2=3.856·(1.5070−1)/0.655=2.98,

and because the optical path difference Φ2 is practically 3 times of thesecond wavelength λ2, the generation of the high degree of sphericalaberration can be suppressed also to the light flux of the secondwavelength λ2, and the transmission factor can be increased.

Further, in order to give high added value to the optical element, andsimultaneously to attain the cost reduction, as in the invention of item15, it is preferable that the optical element is formed of one element,and the superposition type diffractive structure and the optical pathdifference grant structure are formed on respective optical functionsurfaces of the element.

As described above, by reducing the light source wavelength, and byincreasing the numerical aperture of the objective optical system, aproblem of the “chromatic spherical aberration” in which the sphericalaberration is changed by the wavelength change, is actualized.Accordingly, as in the invention of item 29, for the purpose by whichthe recording/reproducing of the information can be adequately conductedfor the high density optical disk, it is preferable that a function bywhich the chromatic aberration generated due to the wavelengthdispersion of the objective optical system is suppressed, is given tothe diffractive structure.

Further, when the objective optical system is structured by plasticlenses, it is advantageous for the cost reduction and weight reduction,however, because the influence of the refractive index change followingthe temperature change becomes large, when the temperature in theoptical pickup device is changed, the recording/reproducing of theinformation for the high density optical disk is interfered. In order tomaintain the good recording/reproducing characteristic, even when thetemperature in the optical pickup device is changed, as in the inventionof item 30, it is preferable that a function by which the sphericalaberration generated due to the refractive index change of the plasticlens is suppressed, is given to the optical path difference grantstructure.

Specifically, as in the invention of item 31, in the case where theoptical path difference grant structure having the temperaturedependency of the spherical aberration by which the spherical aberrationadded to the light flux of the first wavelength λ1 is changed to theunder correction direction when the refractive index is loweredfollowing the environmental temperature rise, and is changed to the overcorrection direction when the refractive index is increased followingthe environmental temperature fall, is formed, the spherical aberrationgenerated in the plastic lens following the temperature change can besuppressed.

In this manner, in a method by which the spherical aberration changefollowing the temperature change of the plastic lens is suppressed bythe optical path difference grant structure, because the sphericalaberration change following the refractive index change of the opticalpath difference grant structure, is used, different from the case by thediffractive structure in which the wavelength dependency is used, evenwhen the wavelength change of the laser light source is not generatedfollowing the temperature change, the suppression effect of thespherical aberration change is actuated.

A specific structure of the is, as in the invention of item 32, astructure is preferable in which, in the ring-shaped zones of theoptical path difference grant structure, the ring-shaped zone of theinner side than the ring-shaped zone positioned at a predeterminedheight within the maximum effective diameter, is shifted to the opticalaxis direction so that, as it is separated from the optical axis, theoptical path length is reduced, and the ring-shaped zone of the outerside than the ring-shaped zone positioned at a predetermined heightwithin the maximum effective diameter, is shifted to the optical axisdirection so that, as it is separated from the optical axis, the opticalpath length is increased, and hereby, the spherical aberration change tothe wavelength change of the incident flux or the spherical aberrationchange following the refractive index change, can be suppressed.

It is preferable that the height from the optical axis at the centralportion of the ring-shaped zone positioned at the predetermined heightis, as in the invention of item 33, the height within the range of 60%to 85% of the maximum effective diameter.

Further, when the structure having the stepped section in the opticalaxis direction such as the superposition type diffractive structure orthe optical path difference grant structure is formed on the opticalelement whose curvature is large, the transmission factor is lowered bythe influence of the shading of the light flux by the stepped sectionportion. In order to prevent such a lowering of the transmission factor,as in the invention written in item 34, it is preferable that theobjective optical system is structured by an aberration correctingelement and a light converging element, and the superposition typediffractive structure and the optical path difference grant structureare formed on the aberration correcting element.

As a specific structure of the superposition type diffractive structure,as in the invention of item 18, it is preferable that the number N ofthe stepped sections formed in each ring-shaped zone is any one of 3 or4 or 5 (that is, each ring-shaped zone is divided by 4, or 5, or 6) andthe optical path difference added to the light flux of the firstwavelength λ1 by the depth Δ of the optical axis direction of thestepped section is practically, 2m times of the first wavelength λ1(where, m is an integer not smaller than 1), hereby, when thesuperposition type diffractive structure, practically, does not give theoptical path difference to the light flux of the first wavelength λ1,but gives the optical path difference to the light flux of the secondwavelength λ2, the light flux of the second wavelength λ2 can beselectively diffracted, and the high transmission factor (diffractionefficiency) can be secured also to the light flux of any wavelength.

As in the invention written in item 19, when the element on which thesuperposition type diffractive structure is formed, is formed of thematerial in which the refractive index to the wavelength λ1 is withinthe range of 1.5-1.6, and Abbe's number in d-line is within the range of50-60, it is preferable that the number of stepped sections N formed ineach ring-shaped zone and the depth D=A (N+1) for one ring-shaped zonestructured by N stepped sections, are set so that they satisfy any oneof expressions (17)-(19).

Hereby, because the 0 degree diffracted light ray which does notpractically give the optical path difference to the light flux of thefirst wavelength λ1, and +1 degree diffracted light ray, when theoptical path difference is given to the light flux of the firstwavelength λ2, can be generated, the spherical aberration generated dueto the difference of the protective layer thickness between the highdensity optical disk and DVD, can be effectively corrected, and the hightransmission factor (diffraction efficiency) can be secured also to thelight flux of any wavelength.

Further, as in the invention of item 36, when the signs B2 and B4 aredifferent from each other, the change amount of h per a unit changeamount of the optical path function φb can be increased. Thiscorresponds to that the minimum width of the ring-shaped zone of thesuperposition type diffractive structure is increased, and the increaseof the transmission factor, and making the metallic mold processing easycan be attained. In order to further attain these effects, it ispreferable that the magnitude of B2 and B4 is set so that the opticalpath difference function φb has the inflection point within theeffective diameter. Herein, the difference of actual shape between acase where the optical path difference function φb has the inflectionpoint within the effective diameter, and a case where it does not havethe inflection point, will be described. In the shape in the case wherethe optical path difference function φb has the inflection point withinthe effective diameter, as shown in FIG. 17, the inclination directionof the ring-shaped zone is switched, forming the ring-shaped zonepositioned at the inflection point (in FIG. 17, 8th ring-shaped zonefrom the inner side) as the boundary. In the shape in the case where theoptical path difference function φb does not have the inflection pointwithin the effective diameter, as shown in FIG. 16, the inclinationdirection of all the ring-shaped zone is the same.

As in the invention written in item 37, in the case where the objectiveoptical system is structured by the aberration correcting element andthe light converging element which is a plastic lens of one group onelens composition, when the paraxial power P1 of the aberrationcorrecting element to the first wavelength λ1 is made positive, thestructure by which the light flux of the first wavelength λ1 enters intothe light converging element as the converging light flux, ispreferable. Generally, NA ∞ (hereinafter, called conversion NA) in whichthe numerical aperture NA of the light converging element of finiteconjugate type (magnification m≠0) is converted into infinite conjugatetype, can be expressed by NA ∞=NA(1−m). Accordingly, in the lightconverging element on which the converging light flux enters (that is,m>0), because the conversion NA can be reduced, the spherical aberrationchange generated in the light converging element following thetemperature change can be suppressed small.

Further, as in the invention of item 38, it is preferable that theparaxial power P1 of the aberration correcting element to the firstwavelength λ1, and the paraxial power P2 of the light converging elementto the first wavelength λ1 are set so that they satisfy the expression(21). In this manner, when the refractive power to the incident lightflux is wholly given to the light converging element arranged on theoptical disk side, the working distance to DVD can be sufficientlysecured. Further, because, on the optical function surface, a structurehaving the stepped section in the optical axis direction such as thesuperposition type diffractive structure is formed, the track is blockedby the stepped section portion, and a ratio of the light flux which doesnot contribute the formation of the light converging spot can besuppressed, and the lowering of the transmission factor can beprevented.

The active effect of item 39 is the same as that of item 112 which willbe described later.

The active effect of item 40 is the same as that of item 114 which willbe described later.

The active effect of item 41 is the same as that of item 113 which willbe described later.

The invention written in item 45 is an optical element for the opticalpickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 projectedfrom the third light source, and it is characterized in that: theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothe third optical information recording medium; and at least one opticalfunction surface in the optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zoneoptical function areas around the optical axis; and on at least oneoptical function area in a plurality of ring-shaped zone opticalfunction areas, the superposition type diffractive structure which is astructure in which a plurality of ring-shaped zones in which apredetermined number of discontinuous stepped sections are formed, arecontinuously arranged around the optical axis, is formed.

According to the invention written in item 45, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function area around the optical axis, and the superpositiontype diffractive structure is formed in the specific optical functionarea, because only one of 3 wavelengths is selectively diffracted, andthe other wavelengths are not diffracted and can be passed as they are,when the arrangement of each ring-shaped zone of the superposition typediffractive structure is adequately set, it is possible that, while thespherical aberration generated due to the difference of the protectivelayer among 3 kinds of optical disks of the high density optical disk,DVD, and CD, is corrected, the high transmission factor (diffractionefficiency) can be secured for all of 3 wavelengths. Further, when thediffraction order of 3 wavelengths is deferred, the degree of freedom ofthe of the optical design is spread, and a role of dichroic filter bywhich, for the specific wavelength, the diffraction efficiency isextremely reduced, specific wavelength is blocked, and the otherwavelengths are transmitted, can be given to the specific wavelength.Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,in 3 kinds of optical disks whose standard is different each other, theworking distance to CDs whose protective layer thickness is largest, canbe sufficiently secured.

Further, because a structure having the minute stepped section such asthe superposition type diffractive structure is formed on the opticalfunction surface of the aberration correcting element, its tack isblocked by the stepped section portion and the rate of the light fluxwhich does not contribute to the formation of the light converging spotcan be suppressed, and the lowering of the transmission factor can beprevented.

The invention written in item 46 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ1) projected from the third light source; and theoptical element is structured by the aberration correcting element, andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothe third optical information recording medium, and in the opticalfunction surfaces of the aberration correcting element, at least oneoptical function surface is divided into a plurality of ring-shapedzone-like optical function areas around the optical axis, and in theplurality of ring-shaped zone-like optical function areas, on theoptical function area including the optical axis, the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones in which a predetermined number of discontinuousstepped sections are formed, are continuously arranged around theoptical axis, is formed, and the first magnification m1 in the casewhere the reproducing and/or recording of the information is conductedfor the first optical information recording medium, and the secondmagnification m2 in the case where the reproducing and/or recording ofthe information is conducted for the second optical informationrecording medium, are almost equal.

According to the invention of item 46, when the optical function surfaceof the aberration correcting element is divided into a plurality ofoptical function areas around the optical axis, and the superpositiontype diffractive structure is formed on the optical function areaincluding the optical axis, because only one of 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted andcan be passed as they are, in the case where the arrangement of eachring-shaped zone of the superposition type diffractive structure isadequately set, when the protective layer thickness of the high densityoptical disk is 0.6 mm which is same as DVD, while the magnification m1for the high density optical disk, and the magnification m2 for DVD arealmost the same, the spherical aberration generated due to thedifference of the protective layer thickness between the high densityoptical disk and DVD can be corrected.

Hereby, a collimator lens for the high density optical disk and acollimator lens for DVD can be common with each other, and further,because a light source module in which the light source for the highdensity optical disk and the light source for DVD are packaged, can beused, the number of optical parts of the optical pickup device can bereduced.

As the stepped section amount Δ of the superposition type diffractivestructure, and the number of stepped sections, it is preferable that itis made a combination as in tables 1-8 which will be described later.

Further, when the refractive power to the incident light flux is whollygiven to the light conversing element arranged on the optical disk side,in 3 kinds of optical disks whose standard is different, the workingdistance to CD whose protective layer thickness is maximum in 3 kinds ofoptical disks whose standard is different, can be assured enough.

Further, because a structure having minute stepped sections such as thesuperposition type diffractive structure is formed on the opticalfunction surface of the aberration correcting element, its track isintercepted by the stepped section portion, and a rate of the light fluxwhich does not contribute to the formation of the light converging spot,can be suppressed, and the lowering of the transmission factor can beprevented.

The invention written in item 47 is characterized in that: in theoptical element for the optical pickup device written in item 46, theparaxial diffraction power of the superposition type diffractivestructure to the second wavelength λ2 is negative.

According to the invention written in item 47, in the case where theprotective layer thickness is thinner than DVD as in the optical diskwhose protective layer thickness is 0.1 mm, when the magnification m1 tothe high density optical disk and the magnification m2 to DVD are madethe same, because the protective layer of the DVD is thick, thespherical aberration to DVD is changed to over correction direction.

In such a case, as in the invention of item 47, when the paraxial powerto the second wavelength λ2 of the superposition type diffractivestructure is made negative, and the light flux of the second wavelengthλ2 is made incident on the light converging element as the diverginglight, by the magnification change of the light converging element, thespherical aberration change to the over correction direction can becancelled.

When such a structure is applied, because the generation of the coma bythe optical axis dislocation of the aberration correcting element andthe light converging lens to the second wavelength λ2 is reduced, aprocess by which the aberration correcting element and the lightconverging lens are integrated, becomes easy.

The invention written in item 48 is characterized in that: in theoptical element for the optical pickup device written in item 47 or 47,the superposition type diffractive structure adds the under correctionspherical aberration to the second wavelength λ2.

Alternatively, as in the invention written in item 48, when thespherical aberration in the under correction direction is added to thesecond wavelength λ2 by the superposition type diffractive structure,the spherical aberration change toward the over correction direction canbe cancelled.

When such a structure is applied, because the coma generated when theslant light flux of the second wavelength λ2 enters, is reduced, as aresult in which the allowance to the optical axis dislocation of thelight source for DVD and the optical element is increased, theproduction cost of the optical pickup device is reduced.

Hereupon, the paraxial power of the superposition type diffractivestructure to the second wavelength λ2 is made negative, and thespherical aberration in the under correction direction may also be madeto be added to the second wavelength λ2 by the superposition typediffractive structure.

The invention written in item 49 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 46 to 48, the first magnification m1 and the second magnificationm2 satisfy the following expression (25).

m1=m2=0  (25)

As in the invention written in item 49, when the magnification m1 to thehigh density optical disk and the magnification m2 to DVD are made 0,even when the optical element is shifted to the track direction of theoptical disk, because there is no change of the object point position,the good tracking characteristic can be obtained.

The invention written in item 50 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 46 to 49, the third magnification m3 when the reproducing and/orrecording of the information is conducted for the third opticalinformation recording medium, satisfies the following expression (26).

−0.25<m3<−0.10  (26)

As will be described later as an example in Tables 1-8, when the steppedsection amount Δ and number of stepped sections N of the superpositiontype diffractive structure are adequately set in such a manner that onlythe second wavelength λ2 is selectively diffracted, and otherwavelengths are not diffracted, and passed as they are, by the action ofthe superposition type diffractive structure, the spherical aberrationchange in the over correction direction generated to CD whose protectivelayer thickness is maximum, can not be corrected. Accordingly, as in theinvention of item 50, when the magnification m3 to CD is made within therange of expression (26), such asphericalal aberration change can becorrected.

Further, when the diverging light flux is made incident on CD, even itis an optical element whose focal distance is small, because the workingdistance to CD can be secured enough, it is advantageous to the sizereduction of the optical pickup device.

The invention written in item 51 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 46 to 50, the first light source and the second light source are apackaged light source module, the optical element light-converges thelight flux of the first wavelength λ1 projected from the light sourcemodule on the information recording surface of the first opticalinformation recording medium, and light-converges the light flux of thesecond wavelength λ2 projected from the light source module on theinformation recording surface of the second optical informationrecording medium.

According to the invention written in item 51, because the magnificationm1 to the high density optical disk and the magnification m2 to DVD arealmost the same, the light source module into which the light source forthe high density optical disk and the light source for DVD are packaged,can be used. Hereby, the number of optical parts of the optical pickupdevice can be reduced.

The invention written in item 52 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; the opticalelement is structured by the aberration correcting element, and thelight converging element for a purpose by which the light flux projectedfrom the aberration correcting element is image-formed on respectiveinformation recording surfaces of the first optical informationrecording medium to the third optical information recording medium; inthe optical function surfaces of the aberration correcting element, atleast one optical function surface is divided into a plurality ofring-shaped zone-like optical function areas around the optical axis; inthe plurality of ring-shaped zone-like optical function areas, in theoptical function area including the optical axis, the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which predetermined number of discontinuousstepped sections are formed, are continuously arranged around theoptical axis, is formed; and the second magnification m2 when thereproducing and/or recording of the information is conducted for thesecond optical information recording medium, and the third magnificationm3 when the reproducing and/or recording of the information is conductedfor the third optical information recording medium, are almostcoincident.

According to the invention written in item 52, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function areas around the optical axis, and when thesuperposition type diffractive structure is formed in the opticalfunction area including the optical axis, because it becomes possiblethat only one of 3 wavelengths is selectively diffracted, and the otherwavelengths are not diffracted, and passed as they are, when thearrangement of each ring-shaped zone of the superposition typediffractive structure is adequately set, while it is made as they arethat the magnification m2 for DVD and the magnification m3 for CD arealmost the same, the spherical aberration generated due to thedifference of the protective layer thickness between DVD and CD, can becorrected.

Hereby, because the light source module into which the light source forDVD and light source for CD are packaged, can be used, the number ofoptical parts of the optical pickup device can be reduced.

As the stepped section amount Δ and the number of stepped sections ofthe superposition type diffractive structure, it is preferable that thecombination as in the above-described Tables 1-8, is applied.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,in three kinds of optical disks whose standard is different, the workingdistance to CD whose protective layer thickness is maximum, can besecured enough.

Further, because, on the optical function surface of the aberrationcorrecting element, a structure having minute stepped sections such asthe superposition type diffractive structure is formed, the track isintercepted by the stepped section portion, and the rate of the lightflux which does not contribute to the formation of the light convergingspot, can be suppressed, and the lowering of the transmission factor canbe prevented.

The invention written in item 53 is characterized in that: in theoptical element for the optical pickup device written in item 52, theparaxial diffraction power of the superposition type diffractivestructure to the second wavelength λ2 is positive.

When the magnification m2 to DVD and the magnification m3 to CD are thesame, because the protective layer of DVD is thinner than that of CD,the spherical aberration to DVD is changed to the under correctiondirection.

In such a case, as in the invention of item 53, when the paraxial powerof the superposition type diffractive structure to the second wavelengthλ2 is made positive, and the light flux of the second wavelength λ2 ismade incident on the light converging element as the converging light,by the magnification change of the light converging element, thespherical aberration change to the under correction direction can becancelled.

When such a structure is applied, because the generation of the coma bythe optical axis dislocation of the aberration correcting element andlight converging lens to the second wavelength λ2 is reduced, a processby which the aberration correcting element and the light converging lensare integrated, becomes easy.

The invention written in item 54 is characterized in that: in theoptical element for the optical pickup device written in item 52 or 53,the superposition type diffractive structure adds the sphericalaberration of over correction to the second wavelength λ2.

Alternatively, as in the invention of item 54, when, by thesuperposition type diffractive structure, the spherical aberrationtoward the over correction direction is added to the second wavelengthλ2, the spherical aberration change toward the under correctiondirection can be cancelled.

When such a structure is applied, because the coma generated when theslant light flux of the second wavelength λ2 enters, is reduced, as aresult in which the allowance to the optical axis dislocation of thelight source for DVD and the optical element is increased, theproduction cost of the optical pickup device is reduced.

Hereupon, the paraxial power of the superposition type diffractivestructure to the second wavelength λ2 is made positive, and by thesuperposition type diffractive structure, the spherical aberrationtoward the over correction direction may also be added to the secondwavelength λ2.

The invention written in item 55 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 52 to 54, the first magnification m1 when the reproducing and/orrecording of the information is conducted for the first opticalinformation recording medium, satisfies the following expression (27).

m1=0  (27)

According to the invention written in item 55, for example, when themagnification m1 to the high density optical disk is made 0, even whenthe optical element is shifted toward the track distance of the opticaldisk, because there is not a change of the object point, the goodtracking characteristic can be obtained.

The invention written in item 56 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 52 to 55, the second magnification m2 and the third magnificationm3 satisfy the following expressions (28) and (29).

m2=m3  (28)

−0.25<m2<−0.10  (29)

As will be described later as an example in Tables 1-8, when the steppedsection amount Δ, and the number of stepped sections are adequately setin such a manner that only the second wavelength λ2 in 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted,and passed as they are, by the action of the superposition typediffractive structure, the spherical aberration change toward the overcorrection direction generated to CD whose protective layer is thickest,can not be corrected. Accordingly, as in the invention of item 56, whenthe magnification m3 to CD is made within the range of the expression(28), such aspherical aberration change can be corrected.

The invention written in item 57 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 52 to 56, the second light source and the third light source are apackaged light source module, and the optical element light-convergesthe light flux of the second wavelength λ2 projected from the lightsource module on the information recording surface of the second opticalinformation recording medium, and light-converges the light flux of thethird wavelength λ3 projected from the light source module on theinformation recording surface of the third optical information recordingmedium.

According to the invention written in item 57, because the magnificationm2 to DVD, and the magnification m3 to CD are made almost the same, thelight source module into which the light source for DVD and the lightsource for CD are packaged, can be used. Hereby, the number of opticalparts of the optical pickup device can be reduced.

The invention written in item 58 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in the optical function areaincluding the optical axis in the plurality of ring-shaped zone-likeoptical function areas; and the first light flux λ1 and the minimumvalue P of the interval in the perpendicular direction to the opticalaxis between adjoining stepped sections in the discontinuous steppedsections formed in each ring-shaped zone in the superposition typediffractive structure, satisfy the following expressions (30) and (31).

0.39 μm<λ1<0.42 μm  (30)

P>3 μm  (31)

According to the invention written in item 58, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function areas around the optical axis, and the superpositiontype diffractive structure is formed in a specific optical functionarea, because it becomes possible that only one of 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted,and passed as they are, when the arrangement of each ring-shaped zone ofthe superposition type diffractive structure is adequately set, whilethe spherical aberration generated due to the difference of theprotective layer thickness among 3 kinds of optical disks such as thehigh density optical disk, DVD, and CD is corrected, the hightransmission factor (diffraction efficiency) to all of 3 wavelengths canbe secured. Further, when the diffraction order of 3 wavelengths is madedifferent, the degree of freedom of optical design is spread, and a roleof the dichroic filter by which, to specific wavelength, the diffractionefficiency is extremely reduced, the specific wavelength is cut-off, andthe other wavelengths are passed, can be charged on it.

Further, the superposition type diffractive structure of the presentinvention has a structure in which each ring-shaped zone is dividedstepwise by a plurality of discontinuous stepped sections in the opticalaxis direction, however, when the interval between adjoining steppedsections, in the direction perpendicular to the optical axis, (width ofeach step structure), is too small, a problem that the metallic moldprocessing by SPDT is difficult, is actualized. Further, the lowering ofthe diffraction efficiency due to the shape error of the metallic moldis larger as the wavelength is shorter.

Accordingly, in the present invention, the minimum value P of the widthof such a step structure is made not larger than 3 μm, the metallic modeprocessing by SPDT is made easy, and the diffraction efficiency loweringdue to the shape error of the metallic mold is made not too large to thewavelength λ1 of the blue violet range.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,the working distance to CD whose protective layer thickness is maximumin three kinds of optical disks whose standard is different, can besecured enough.

Further, because a structure having the minute stepped section such asthe superposition type diffractive structure is formed on the opticalfunction surface of the aberration correcting element, the track is cutoff by the stepped section portion and a rate of light flux which doesnot contribute to the formation of light converging spot, can besuppressed, and the lowering of the transmission factor can beprevented.

The invention written in item 59 is characterized in that: in theoptical element for the optical pickup device written in item 58, in thediscontinuous stepped section formed in each ring-shaped zone in thesuperposition type diffractive structure, the minimum value P of theinterval in the direction perpendicular to the optical axis betweenadjoining stepped sections satisfies the following expression (32).

P>5 μm  (32)

As in the invention written in item 59, in order to make the effect moreeffective, it is preferable that the minimum value P of the width of thestep structure is made larger than 5 μm.

The invention written in item 60 is characterized in that: in theoptical element for the optical pickup device written in item 58, in thediscontinuous stepped section formed in each ring-shaped zone in thesuperposition type diffractive structure, the minimum value P of theinterval in the direction perpendicular to the optical axis betweenadjoining stepped sections satisfies the following expression (33).

P>10 μm  (33)

As in the invention written in item 60, in order to make the effect moreeffective, it is preferable that the minimum value P of the width of thestep structure is made larger than 10 μm.

The invention written in item 61 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in the optical function areaincluding the optical axis in the plurality of ring-shaped zone-likeoptical function areas; and when the optical path difference added tothe transmission wave-front by the superposition type diffractivestructure is defined by the arith. 1, signs of B2 and B4 are differentfrom each other.

According to the invention of item 61, when signs of B2 and B4 are madedifferent from each other, the change amount of h per unit change amountof the optical path function φb can be made large. This corresponds to acase where the minimum width of the ring-shaped zone of thesuperposition type diffractive structure is increased, and the increaseof the transmission factor and to make easy the metallic mold processingcan be attained. In order to further attain these effects, it ispreferable that magnitudes of B2 and B4 are set so that the optical pathfunction φb has the inflection point.

The invention written in item 62 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 58 to 61, the first magnification m1 in the case where thereproducing and/or recording of the information is conducted for thefirst optical information recording medium, the second magnification m2in the case where the reproducing and/or recording of the information isconducted for the second optical information recording medium, and thethird magnification m3 in the case where the reproducing and/orrecording of the information is conducted for the third opticalinformation recording medium, are different form each other.

When it is tried to largely secure the minimum value P of the width ofthe step structure, the aberration correction effect by thesuperposition type diffractive structure can not be obtained enough, anda problem that the spherical aberration generated due to the differenceof the protective layer thickness among 3 kinds of optical disks such asthe high density optical disk, DVD, and CD, can not be corrected, isactualized. Accordingly, as in the invention of item 62, it ispreferable that the magnification m1 for the high density optical disk,the magnification m2 for DVD, and the magnification m3 for CD are madedifferent from each other, and the spherical aberration remained withoutbeing corrected, is corrected.

The invention written in item 63 is characterized in that: in theoptical element for the optical pickup device written in item 62, thefirst magnification m1, the second magnification m2 and the thirdmagnification m3 satisfy the following expressions (34) to (36).

m1=0  (34)

−0.08<m2<−0.01  (35)

−0.25<m3<−0.10  (36)

Specifically, as the magnification m1 to the high density optical disk,the magnification m2 to DVD, and the magnification m3 to CD, as in theinvention of item 63, it is preferable that they are within the range ofexpressions (34)-(36).

The invention written in item 64 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in at least one optical function areain the plurality of ring-shaped zone-like optical function areas; and inthe superposition type diffractive structure, either one of the number Nof the discontinuous stepped sections formed in each ring-shaped zone,or the depth Δ (μm) in the optical axis direction of the discontinuousstepped section, is different for each optical function area.

According to the invention written in item 64, in the case where theoptical function surface of the aberration correcting element is dividedinto a plurality of optical function areas around the optical axis, andthe superposition type diffractive structures are formed in theplurality of optical function areas, and either one of the number ofdiscontinuous stepped section formed in each ring-shaped zone, or thedepth Δ (μm) in the optical axis direction of the discontinuous steppedsection, is made different for each optical function area, when thediffraction order of 3 wavelengths is made different, a role of thedichroic filter by which the degree of freedom of the optical design isspread, or the diffraction efficiency is extremely reduced to thespecific wavelength, and the specific wavelength is cut off and theother wavelengths are passed, can be charged on it.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,the working distance to CD whose protective layer thickness is maximumin 3 kinds of optical disks whose standard is different, can be securedenough.

Further, because a structure having the minute stepped section such asthe superposition type diffractive structure is formed on the opticalfunction surface of the aberration correcting element, the track is cutoff by the stepped section portion, and a rate of the light flux whichdoes not contribute to the formation of the light converging spot, canbe suppressed, and the lowering of the transmission factor can beprevented.

The invention written in item 65 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in at least one optical function areain the plurality of ring-shaped zone-like optical function areas; and inoptical function surfaces of the aberration correcting element, on atleast one optical function surface, the diffractive structure formed ofa plurality of ring-shaped zones divided by the stepped section aroundthe optical axis, is formed.

The invention written in item 66 is characterized in that: in theoptical element for the optical pickup device written in item 65, thedepth of the stepped section of the diffractive structure is designed insuch a manner that, to the diffraction order n1 of the diffracted lightray having the maximum diffraction efficiency in the diffracted lightray generated when the light flux of the first wavelength λ1 enters, thediffraction order n2 of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the second wavelength λ2 enters, the diffraction order n3of the diffracted light ray having the maximum diffraction efficiency inthe diffracted light ray generated when the light flux of the thirdwavelength λ3 enters, are both lower degree.

The invention written in item 67 is characterized in that: in theoptical element for the optical pickup device written in item 66, thefirst wavelength λ 1 (μm), second wavelength λ2 (μm), third wavelengthλ3 (μm), respectively satisfy the following expressions (37) to (39),and a combination of the diffraction order n1, the diffraction order n2,and the diffraction order n3, is any one of (n1, n2, n3)=(2, 1, 1), (4,2, 2), (6, 4, 3), (8, 5, 4), (10, 6, 5).

0.39<λ1<0.42  (37)

0.63<λ2<0.68  (38)

0.75<λ3<0.85  (39)

The invention written in item 68 is characterized in that: in theoptical element for the optical pickup device written in item 67 or 67,the aberration correcting element is formed of the material in which therefractive index at the first wavelength λ1 is within the range of1.5-1.6, and Abbe's number in d-line is within the range of 50-60, andthe depth d1 in the optical axis direction of the stepped sectionclosest to the optical axis in the stepped sections of the diffractivestructure, satisfies any one of the following expressions (40) to (44).

1. 2 μm>d1>1.7 μm  (40)

2. 6 μm>d1>3.0 μm  (41)

4. 4 μm<d1<5.0 μm  (42)

5. 6 μm<d1<6.5 μm  (43)

6. 9 μm>d1>8.1 μm  (44)

The invention written in item 69 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 65 to 68, the diffractive structure has a function to suppress thefocus position dislocation generated due to the chromatic aberration ofthe light converging element when the first wavelength λ1 is changedwithin the range of ±10 nm.

The invention written in item 70 is characterized in that: in theoptical element for the optical pickup device written in item 69, thediffractive structure has a function to suppress the chromaticaberration on axis generated due to the chromatic aberration of thelight converging element when the first wavelength λ1 is changed withinthe range of ±10 nm.

The invention written in item 71 is characterized in that: in theoptical element for the optical pickup device written in item 69 or 70,the diffractive structure has a function to suppress the sphericalaberration change generated due to the chromatic aberration of the lightconverging element when the first wavelength λ1 is changed within therange of ±10 nm.

The invention written in item 72 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 65 to 71, the light converging element is formed of a plasticlens, and when the diffractive structure has the wavelength dependencyin which the spherical aberration changes toward the under correctiondirection when the first wavelength λ1 changes to long wavelength side,and the spherical aberration changes toward the over correctiondirection when the first wavelength λ1 changes to short wavelength side,the diffractive structure has a function to suppress the sphericalaberration change generated due to the refractive index change of thelight converging element following the environmental temperature change.

The invention written in item 73 is characterized in that: in theoptical element for the optical pickup device written in item 72, atleast one optical function surface in the optical function surfaces ofthe aberration correcting element, is divided into a central opticalfunction area including the optical axis, and a peripheral opticalfunction area which surrounds the periphery of the central opticalfunction area, and the diffractive structure is formed only in theperipheral optical function area.

The invention written in item 74 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 65 to 73, the sectional shape of the diffractive structureincluding the optical axis is the stepped shape.

The invention written in item 75 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 65 to 73, the sectional shape of the diffractive structureincluding the optical axis is the saw-toothed shape.

The invention written in item 76 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 65 to 75, the superposition type diffractive structure is formedon one optical function surface of the aberration correcting element,and the diffractive structure is formed on the other optical functionsurface of the aberration correcting element.

According to the invention written in item 65, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function areas around the optical axis, and the superpositiontype diffractive structure is formed in the specific optical functionarea, because it becomes possible that only one of 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted andpassed as they are, when the arrangement of each ring-shaped zone of thesuperposition type diffractive structure is adequately set, while thespherical aberration generated due to the difference of the protectivelayer thickness among 3 kinds of optical disks such as the high densityoptical disk, DVD, and CD, is corrected, the high transmission factor(diffraction efficiency) can be secured to all of 3 wavelengths.Further, when the diffraction order of 3 wavelengths is made different,a role of the dichroic filter by which the degree of freedom of theoptical design is spread, the diffraction efficiency is extremelyreduced to the specific wavelength, the specific wavelength is cut off,and the other wavelengths are passed, can be charged on it.

Further, in order to enable to adequately conduct therecording/reproducing of the information for the high density opticaldisk, it is necessary that, when a means for correcting the chromaticaberration is provided, the deterioration of the light convergingperformance by the instantaneous wavelength change of the laser lightsource, which is called mode-hopping, is prevented. This is for thereason that, because the wavelength dispersion of the lens materialbecomes very large in the blue violet region, the focus positiondislocation is largely generated also to a slight wavelength change.

Further, as a standard of the high density optical disk, an optical diskin which NA of the objective lens is increased to about 0.85, isproposed, however, because NA of the optical element is more increased,the larger the spherical aberration change generated by the wavelengthchange of the incident light flux is, a problem that the laser lightsource having the wavelength error by the production error can not beused, is actualized. Therefore, because it is necessary that the laserlight source is selected, the production cost of the optical pickupdevice is increased.

Hereupon, because the specific gravity of the plastic lens is smallerthan the glass lens, the load onto the actuator for driving theobjective optical system can be reduced, and the follow-up of theobjective optical system can be conducted at high speed. Further, in theplastic lens produced by the injection molding, when a desired metallicmold is accurately produced, the mass-production can be high-accuratelyconducted with the stable quality. However, in the case where NA of theobjective optical system is increased, when such an objective opticalsystem is made plastic lens, the influence of the refractive indexchange following the temperature change becomes large. This is for thereason that the spherical aberration generated by the refractive indexchange is increased in proportion to the fourth power of NA.

Accordingly, in the present invention, when the diffractive structure isprovided on the optical function surface of the aberration correctingelement, because the focus position dislocation to the wavelength changeof the incident light flux generated in the light converging element,the spherical aberration change to the wavelength change of the incidentlight flux, or the spherical aberration change following the refractiveindex change are suppressed, even when the wavelength change of theincident light flux or the temperature change occurs, therecording/reproducing characteristic to the high density optical diskcan be maintained good.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on optical disk side, theworking distance to CD whose protective layer thickness is maximum in 3kinds of optical disks whose standard is different, can be securedenough.

Further, because, on the optical function surface of the aberrationcorrecting element, a structure having the minute stepped sections suchas the superposition type diffractive structure or the diffractivestructure, is formed, the track is cut off by the stepped sectionportion, and a rate of the light flux which does not contribute to theformation of the light converging spot, can be suppressed, and thelowering of the transmission factor can be prevented.

However, because, in the light source for the high density optical disk,and the light source for DVD or CD, the wavelength difference is large,when the same degree diffracted light ray generated in the diffractivestructure is used as the light flux for recording/reproducing torespective optical disks, the enough diffraction efficiency can not beobtained to 3 wavelengths. For such a problem, as in the invention ofitem 66, when the diffractive structure is designed in such a mannerthat the diffraction order n2 of the diffracted light ray used for DVD,and the diffraction order n3 of the diffracted light ray used for CD,are lower degree than the diffraction order n1 of the diffracted lightray used for the high density optical disk, the diffraction efficiencyto 3 wavelengths can be secured enough.

Specifically, when a combination as in the invention of item 67 isapplied, as the diffraction orders n1, n2, n3, it is preferable becausethe high diffraction efficiency can be secured to all wavelengths of thewavelength λ1-λ3.

When the aberration correcting element is formed of the material inwhich the refractive index to the wavelength λ1 is within the range of1.5-1.6, and Abbe's number in d-line is within the range of 50-60, as inthe invention of item 68, when the depth d1 of the stepped sectionpositioned at the position closest to the optical axis in the steppedsections of the diffractive structure is set so that it satisfies anyone of expressions (40)-(44), the high diffraction efficiency can besecured to all of wavelengths λ1-λ3. Hereupon, the combination of thediffraction orders n1, n2, n3 and the stepped section d1 have arelationship in which (n1, n2, n3)=(2, 1, 1) corresponds to theexpression (40), (n1, n2, n3)=(4, 2, 2) corresponds to the expression(41), (n1, n2, n3)=(6, 4, 3) corresponds to the expression (42), (n1,n2, n3)=(8, 5, 4) corresponds to the expression (43), and (n1, n2,n3)=(10, 6, 5) corresponds to the expression (44).

Generally, in the optical pickup device, a case where the information isrecorded to the optical disk, requires larger laser power than a casewhere the information is reproduced. Therefore, when the information isswitched from the reproducing to recording, there is a case where thewavelength change is caused following the laser power change (modehopping). By such a mode hopping, because the focus position dislocationis generated in the objective optical system, the defocus condition iscontinued until the focus servo corresponds. In the invention of item69, because it is structured so that the focus position dislocation inthe blue violet region of the light converging element is suppressed bythe diffractive structure of the aberration correcting element, evenwhen the blue violet laser light source causes the mode hopping, thegood light converging performance can be maintained.

In order to suppress the focus position dislocation in the blue violetregion of the light converging element, specifically, as in theinvention of item 70, it is preferable that the light converging elementis structured so that, when the paraxial power of the diffractivestructure is made positive, the chromatic aberration on axis issuppressed.

Further, in order to suppress the spherical aberration change generatedin the light converging element by the wavelength change of the incidentlight flux, which is actualized when NA of the optical element isincreased, specifically, as in the invention of item 72, it ispreferable that, when the wavelength dependency in which, when thewavelength of the incident light flux is increased, the sphericalaberration changes toward the under correction direction, and when thewavelength of the incident light flux is reduced, the sphericalaberration changes toward the over correction direction, is given to thediffractive structure, the spherical aberration generated in the lightconverging element is suppressed.

Further, in order to suppress the spherical aberration change generatedin the light converging element which is a plastic lens, by therefractive index change, actualized when NA of the optical element isincreased, it is preferable that, the wavelength dependency of thespherical aberration in which, when the wavelength of the incident lightflux is increased, the spherical aberration changes toward the undercorrection direction, and when the wavelength of the incident light fluxis reduced, the spherical aberration changes toward the over correctiondirection, is given to the diffractive structure. In the lightconverging element which is a plastic lens, because when the temperaturerises, the refractive index is lowered, the spherical aberration changestoward the over correction direction, and when the temperature falls,because the refractive index is increased, the spherical aberrationchanges toward the under correction direction. On the one hand, thelaser light source has a characteristic in which, when the temperaturerises, the wavelength is increased, and when the temperature falls, thewavelength is reduced. When this characteristic is used, when thewavelength dependency of the above-described spherical aberration isspherical aberration change generated in the light converging elementgiven to the diffractive structure, the can be cancelled. Hereupon, inorder to effectively suppress the spherical aberration change generatedin the light converging element, it is preferable that the diffractivestructure is formed on the aspherical surface.

The diffractive structure to suppress the spherical aberration changegenerated in the light converging element is used to form the spot onthe information recording surfaces of 3 optical disks. When it is formedin common optical function area of the light fluxes of 3 wavelengths, itis necessary to form the diffractive structure as in the invention ofitems 66 to 68. In such a case, it is impossible in the principle thatthe diffraction efficiency is made 100% to all of 3 wavelengths.Accordingly, as in the invention of item 73, it is preferable that theoptical function surface of the aberration correcting element is dividedinto the central optical function area including the optical axis, andthe peripheral optical function area which surrounds the periphery ofthis central optical function area, and only in the peripheral opticalfunction area, the diffractive structure is formed. For example, in thecase where this peripheral optical function area is the optical functionarea (for example, NA 0.60-NA 0.85) corresponding to NA from NA of DVDto NA of the high density optical disk, when the optimizing wavelengthof the diffractive structure is made coincident to the wavelength λ1,the diffraction efficiency to the wavelength λ1 can be made 100%, andfurther, the transmission factor to the wavelength λ2 and wavelength λ3in the central optical function area which is made the continuousaspherical surface on which the diffractive structure is not formed, canbe made high. Because the spherical aberration is increased inproportion to 4th power of NA, even though the diffractive structure isnot formed in the central optical function area whose NA is small, thespherical aberration can be effectively corrected by the diffractivestructure of the peripheral optical function area.

As a specific shape of such a diffractive structure, as in the inventionwritten in item 74, a shape in which the sectional shape including theoptical axis is stepped shape, is listed.

Further, as a specific shape of such a diffractive structure, as in theinvention written in item 75, the sectional shape including the opticalaxis may also be the saw-toothed shape.

In order to make the processing of the metallic mold of the aberrationcorrecting element easy, as in the invention of item 76, it ispreferable that the superposition type diffractive structure and thediffractive structure are respectively formed on another opticalfunction surface.

The invention written in item 77 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in at least one optical function areain the plurality of ring-shaped zone-like optical function areas; and inoptical function surfaces of the aberration correcting element, on atleast one optical function surface, the optical path difference grantstructure structured by a plurality of ring-shaped zones divided by thestepped section, in the central area including the optical axis, andoutside the central area, is formed.

According to the invention written in item 77, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function areas around the optical axis, and the superpositiontype diffractive structure is formed on the specific optical functionarea, because it becomes possible that only one of 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted andpassed as they are, when the arrangement of each ring-shaped zone of thesuperposition type diffractive structure is adequately set, while thespherical aberration generated due to the difference of the protectivelayer thickness among 3 kinds of optical disks such as the high densityoptical disk, DVD, and CD, is corrected, the high transmission factor(diffraction efficiency) to all of 3 wavelengths can be secured.Further, when the diffraction order of 3 wavelengths is made different,a role of the dichroic filter by which the degree of freedom of theoptical design is spread, the diffraction efficiency is extremelyreduced to the specific wavelength, the specific wavelength is cut off,and the other wavelengths are passed, can be charged on it.

Further, in the present invention, when the optical path differencegrant structure is provided on the optical function surface of theaberration correcting element, because the focus position dislocation tothe wavelength change of the incident light flux generated in the lightconverging element, the spherical aberration change to the wavelengthchange of the incident light flux, or the spherical aberration changefollowing the refractive index change is suppressed, even when thewavelength change of the incident light flux or temperature change iscaused, the recording/reproducing characteristic to the high densityoptical disk can be maintained good.

Further, when the stepped section amount between adjoining ring-shapedzones of the optical path difference grant structure is adequately set,in the same manner as the above-described superposition type diffractivestructure, because a function by which the spherical aberrationgenerated due to the difference of the protective layer thickness amonga plurality of kinds of optical disks whose protective layer thicknessis different, is suppressed, is given, the degree of freedom of thedesign of optical disk of the present invention can be increased.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,the working distance to CD whose protective layer thickness is maximumin 3 kinds of optical disks whose standard is different, can be securedenough.

Further, because a structure having the minute stepped section such asthe superposition type diffractive structure or optical path differencegrant structure is formed on the optical function surface of theaberration correcting element, the track is cut off by the steppedsection portion, and a rate of the light flux which does not contributeto the formation of the light converging spot, can be suppressed, andthe lowering of the transmission factor can be prevented.

The invention written in item 78 is characterized in that: in theoptical element for the optical pickup device written in item 77, bothof the light converging element and the aberration correcting elementare plastic lenses, and when the optical path difference grant structurehas the temperature dependency of the spherical aberration in which,when the environmental temperature rises, the spherical aberration to beadded to the first wavelength λ1 changes toward the under correctiondirection, and when the environmental temperature falls, the sphericalaberration to be added to the first wavelength λ1 changes toward theover correction direction, it has a function by which the sphericalaberration change generated by the refractive index change of the lightconverging element following the environmental temperature change issuppressed.

The invention written in item 79 is characterized in that: in theoptical element for the optical pickup device written in item 78, in theoptical path difference grant structure, the ring-shaped zone adjoiningthe outside of the central area is formed by shifting to the opticalaxis direction so that the optical path length is reduced to the centralarea, and the ring-shaped zone at the maximum effective diameterposition is formed by shifting to the optical axis direction so that theoptical path length is increased to the ring-shaped zone adjoining itsinside, and the ring-shaped zone at the position of 75% of the maximumeffective diameter is formed by shifting to the optical axis directionso that the optical path length is reduced to the ring-shaped zoneadjoining its inside and the ring-shaped zone adjoining its outside.

The invention written in item 80 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 77 to 79, by the first wavelength λ1 (μm), the second wavelengthλ2 (μm), the third wavelength λ3 (μm), the depth d2 (μm) in the opticalaxis direction of the stepped section closest to the optical axis instepped sections of the optical path difference grant structure, therefractive index Nλ1 to the first wavelength λ1 of the aberrationcorrecting element, the refractive index Nλ2 to the second wavelength λ2of the aberration correcting element, and the refractive index Nλ3 tothe third wavelength λ3 of the aberration correcting element, Φ1, Φ2, Φ3respectively expressed by the following expressions (45) to (47) satisfythe following expressions (48) to (51).

Φ1=d2(Nλ1−1)/λ1  (45)

Φ2=d2(Nλ2−1)/λ2  (46)

Φ3=d2(Nλ3−1)/λ3  (47)

INT(Φ1)<10  (48)

0≦|INT(Φ1)−Φ1|≦0.4  (49)

0≦|INT(Φ2)−Φ2|≦0.4  (50)

0≦|INT(Φ3)−Φ3|≦0.4  (51)

Where, INT (Φi) (i=1, 2, 3) is an integer obtained by half-adjusting (i.

The invention written in item 78 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 77 to 80, the superposition type diffractive structure is formedon one optical function surface of the aberration correcting element,and the optical path difference grant structure is formed on the otheroptical function surface of the aberration correcting element.

According to the invention written in item 78, in order to suppress thespherical aberration change generated by the refractive index change ofthe light converging element which is a plastic lens, when theaberration correcting element is mad a plastic lens, and the opticalpath difference grant structure having the refractive index dependencyof the spherical aberration by which, when the refractive index isreduced, the spherical aberration changes to the under correctiondirection, and when the refractive index is increased, the sphericalaberration changes to the over correction direction, is formed, thespherical aberration change generated in the light converging elementfollowing the temperature change can be cancelled. Hereby, even when NAof the optical element is increased, an optical element in which achange of recording/reproducing characteristic to the high densityoptical disk following the temperature change is small, can be provided.

Further, as in the present invention, when the spherical aberrationchange following the temperature change is suppressed by the opticalpath difference grant structure, because the refractive index change ofthe aberration correcting element is used, different from the case wherethe spherical aberration change of the light converging element issuppressed by using the wavelength dependency of the diffractivestructure, even when the wavelength change of the laser light source isnot caused, the suppression effect of the spherical aberration isactuated.

The specific structure of such a optical path difference grant structureis, as in the invention written in item 79, a structure in which thering-shaped zone adjoining the outside of the central area is formed byshifting to the optical axis direction so that the optical path lengthis reduced to the central area, and the ring-shaped zone at the maximumeffective diameter position is formed by shifting to the optical axisdirection so that the optical path length is increased to thering-shaped zone adjoining its inside, and the ring-shaped zone at theposition of 75% of the maximum effective diameter is formed by shiftingto the optical axis direction so that the optical path length is reducedto the ring-shaped zone adjoining its inside and the ring-shaped zoneadjoining its outside. When such a structure is applied, the refractiveindex dependency of the spherical aberration by which, when therefractive index is lowered, the spherical aberration changes toward theunder correction direction, and when the refractive index is increased,the spherical aberration changes toward the over correction direction,can be given to the optical path difference grant structure.

When the above-described optical path difference grant structure isformed in the common optical function area of the light flux of 3wavelengths used for forming the spot on the information recordingsurfaces of 3 optical disks, as in the invention of item 80, it ispreferable that the depth d2 of the stepped section at the positionclosest to the optical axis, and the optical path differences Φ1-Φ3added to each of wavelengths λ1-λ3 by the stepped section are set sothat they satisfy expressions (45)-(51).

When these expression are not satisfied, because the wavelengthdifference is large between the light source for the high densityoptical disk and the light source for DVD or CD, the high degree of thespherical aberration is generated to any one of wavelengths. Although itis said that the high degree of spherical aberration does not influenceon the recording/reproducing performance, it is practically equivalentto the lowering of the transmission factor. When these expressions aresatisfied, the generation of high degree of spherical aberration can besuppressed, and the transmission factor can be increased.

In order to make the processing of the metallic mold of the aberrationcorrecting element easy, as in the invention of item 81, it ispreferable that the superposition type diffractive structure and theoptical path difference grant structure are respectively formed onanother optical function surface.

The invention written in item 82 is characterized in that: it is anoptical element for the optical pickup device by which the reproducingand/or recording of the information is conducted for the first opticalinformation recording medium having the protective layer of thickness t1by using the light flux of the first wavelength λ1 projected from thefirst light source, the reproducing and/or recording of the informationis conducted for the second optical information recording medium havingthe protective layer of thickness t2 (t2≧t1) by using the light flux ofthe second wavelength λ2 (λ2>λ1) projected from the second light source,and the reproducing and/or recording of the information is conducted forthe third optical information recording medium having the protectivelayer of thickness t3 (t3>t2) by using the light flux of the thirdwavelength λ3 (λ3>λ2) projected from the third light source; and theoptical element is structured by the aberration correcting element andthe light converging element by which the light flux projected from theaberration correcting element is image-formed on respective informationrecording surfaces of the first optical information recording medium tothird optical information recording medium; the light converging elementis a plastic lens of 1-group 1-lens composition; at least one opticalfunction surface in optical function surfaces of the aberrationcorrecting element is divided into a plurality of ring-shaped zone-likeoptical function areas around the optical axis; the superposition typediffractive structure which is a structure in which a plurality ofring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed in at least one optical function areain the plurality of ring-shaped zone-like optical function areas; andthe paraxial power P1 (mm⁻¹) of the aberration correcting element to thefirst wavelength λ1 satisfies the following expression (52).

P1>0  (52)

The invention written in item 83 is characterized in that: in theoptical element for the optical pickup device written in item 82, theaberration correcting element is a plastic lens, and the paraxialrefractive power PR (mm⁻¹) of the aberration correcting elementsatisfies the following expression (53).

PR>0  (53)

The invention written in item 84 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 83, the optical function area in which the superpositiontype diffractive structure is formed, is the optical function areaincluding the optical axis.

The invention written in item 85 is characterized in that: in theoptical element for the optical pickup device written in item 84, in thefirst wavelength λ1 (μm), second wavelength λ2 (μm), third wavelength λ3(μm), the superposition type diffractive structure formed in the opticalfunction area including the optical axis, by the number N ofdiscontinuous stepped sections formed in each ring-shaped zone, thedepth Δ (μm) in the optical axis direction of the discontinuous steppedsection, the refractive index Nλ1 to the first wavelength λ1 of theaberration correcting element, refractive index Nλ2 to the secondwavelength λ2 of the aberration correcting element, and refractive indexNλ3 to the third wavelength λ3 of the aberration correcting element, φ1,φ2, φ3 respectively expressed by the following expressions (54) to (56)satisfy the following expressions (57) to (59).

φ1=Δ(Nλ1−1)(N+1)/λ1  (54)

φ2=Δ(Nλ2−1)(N+1)/λ2  (55)

φ3=Δ(Nλ3−1)(N+1)/λ3  (54)

0≦|INT(Φ1)−Φ1|≦0.4  (57)

0≦|INT(Φ2)−Φ2|≦0.4  (58)

0≦|INT(Φ3)−Φ3|≦0.4  (59)

Where, INT (Φi) (i=1, 2, 3) is an integer obtained by half-adjusting Φi.

The invention written in item 86 is characterized in that: in theoptical element for the optical pickup device written in item 85, Φ1 andthe number N of discontinuous stepped sections formed in eachring-shaped zone satisfy the following expressions (60) and (61).

Φ1≦24  (60)

3<N<11  (61)

The invention written in item 87 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 84 to 86, the superposition type diffractive structure formed inthe optical function area including the optical axis, gives anequivalent first optical action to the light flux of the firstwavelength λ1 and the light flux of the third wavelength λ3, and to thelight flux of the second wavelength λ2, the second optical action whichis different from the first optical action, is given.

The invention written in item 88 is characterized in that: in theoptical element for the optical pickup device written in item 87, thefirst optical action is 0-degree diffraction which does not practicallygive the optical path difference in between adjoining ring-shaped zonesto the light flux of the first wavelength λ1 and the light flux of thethird wavelength λ3, and the second optical action is the first degreediffraction by which the light flux of the second wavelength λ2 isdiffracted to the first degree direction.

The invention written in item 89 is characterized in that: in theoptical element for the optical pickup device written in item 88, theaberration correcting element is formed of the material in which therefractive index in the first wavelength λ1 is within the range of1.5-1.6, and Abbe's number on d-line is within the range of 50-60, andthe first wavelength λ1 (μm), second wavelength λ2 (μm), and thirdwavelength λ3 (μm) respectively satisfy the following expressions (62)to (64), and in the superposition type diffractive structure formed inthe optical function area including the optical axis, a combination ofthe number N of discontinuous stepped sections formed in eachring-shaped zone, and the depth D (μm) in the optical axis direction ofthe ring-shaped zone, is respectively any one of the followingexpressions (65)-(68).

0.39<λ1<0.42  (62)

0.63<λ2<0.68  (63)

0.75<λ3<0.85  (64)

When N=3, 4.1≦D≦4.8  (65)

When N=4, 5.4≦D≦6.4  (66)

When N=5, 7.0≦D≦7.9  (67)

When N=6, 8.4≦D≦9.0  (68)

The invention written in item 90 is characterized in that: in theoptical element for the optical pickup device written in item 87, thefirst optical action is 0-degree diffraction by which the optical pathdifference is not practically given in between adjoining ring-shapedzones to the light flux of the first wavelength λ1 and the light flux ofthe third wavelength λ3, and the second optical action is thesecond-degree diffraction by which the light flux of the secondwavelength λ2 is diffracted in the second-degree direction.

The invention written in item 91 is characterized in that: in theoptical element for the optical pickup device written in item 90, theaberration correcting element is formed of the material in which therefractive index in the first wavelength λ1 is within the range of1.5-1.6, and Abbe's number on d-line is within the range of 50-60, andthe first wavelength λ1 (μm), second wavelength λ2 (μm), and thirdwavelength λ3 (μm) respectively satisfy the following expressions (69)to (71), and in the superposition type diffractive structure formed inthe optical function area including the optical axis, the number N ofdiscontinuous stepped sections formed in each ring-shaped zone, and thedepth D (μm) in the optical axis direction of the ring-shaped zone, arerespectively any one of the following expressions (72)-(75).

0.39<λ1<0.42  (69)

0.63<λ2<0.68  (70)

0.75<λ3<0.85  (71)

When N=8, 11.3≦D≦12.7  (72)

When N=9, 12.8≦D≦14.1  (73)

When N=10, 14.2≦D≦15.6  (74)

When N=11, 15.7≦D≦17.2  (75)

The invention written in item 92 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 84 to 91, the superposition type diffractive structures are formedin all of the plurality of optical function areas.

The invention written in item 93 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 91, the superposition type diffractive structure is notformed in at least one optical function area of the plurality of opticalfunction areas.

The invention written in item 94 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 93, the superposition type diffractive structures are formedon a plurality of optical function surfaces of the aberration correctingelement.

The invention written in item 95 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 94, the thickness t1 of the protective layer of the firstoptical information recording medium, and the thickness t2 of theprotective layer of the second optical information recording medium,satisfy the following expression (76).

0.8≦t1/t2<1.2  (76)

The invention written in item 96 is characterized in that: in theoptical element for the optical pickup device written in item 95, theplurality of optical function areas are 2 optical function areas, thelight fluxes which enters into the optical function area including theoptical axis, in 2 optical function areas, of the first wavelength λ1 tothe third wavelength λ3, respectively form good wave-fronts on theinformation recording surfaces of the first information recording mediumto the third information recording medium, and the light fluxes of thefirst wavelength λ1 and the second wavelength λ2 which are incident onthe optical function area not including the optical axis in 2 opticalfunction areas, respectively form good wave-fronts on the informationrecording surfaces of the first optical information recording medium andthe second optical information recording medium.

The invention written in item 97 is characterized in that: in theoptical element for the optical pickup device written in item 96, in 2optical function areas, in the optical function area not including theoptical axis, the superposition type diffractive structure is formed,and the diffraction efficiency η3 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the third wavelength λ3 enters into thesuperposition type diffractive structure, is not larger than 40%.

The invention written in item 98 is characterized in that: in theoptical element for the optical pickup device written in item 96 or 97,in 2 optical function areas, when the superposition type diffractivestructure is formed in the optical function area not including theoptical axis, and the superposition type diffractive structure gives anequivalent optical action to the light flux of the first wavelength λ1and the light flux of the second wavelength λ2, and gives the opticalaction different from the above-described optical action to the lightflux of the third wavelength λ3, the light flux of the third wavelengthλ3 transmitted the superposition type diffractive structure is made aflare component which does not contribute to the spot formation onto theinformation recording surface of the third optical information recordingmedium. Here, The expression “a flare component which does notcontribute to the spot formation onto an information recording surface”means to make a light flux to be in a situation that the light flux hasan aberration of 0.1 λrms or more on a prescribed information recordingsurface.

The invention written in item 99 is characterized in that: in theoptical element for the optical pickup device written in item 95, theplurality of optical function areas are 3 optical function areas, and in3 optical function areas, the light flux of the first wavelength λ1 tothe light flux of the third wavelength λ3 which are incident on theoptical function area including the optical axis respectively form goodwave-fronts on the information recording surfaces of the first opticalinformation recording medium to the third optical information recordingmedium, and in 3 optical function areas, the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2 which areincident on the optical function area adjoining the outside of theoptical function area including the optical axis, respectively form goodwave-fronts on the information recording surfaces of the first opticalinformation recording medium and the second optical informationrecording medium, and in 3 optical function areas, the light flux of thefirst wavelength λ1 which enters into the most outside optical functionarea, forms a good wave-front on the information recording surface ofthe first optical information recording medium.

The invention written in item 100 is characterized in that: in theoptical element for the optical pickup device written in item 99, in theoptical function area adjoining the outside of the optical function areaincluding the optical axis in 3 optical function areas, thesuperposition type diffractive structure is formed, and the diffractionefficiency η3 of the diffracted light ray having the maximum diffractionefficiency in the diffracted light ray generated when the light flux ofthe third wavelength λ3 enters into the superposition type diffractivestructure is not larger than 40%.

The invention written in item 101 is characterized in that: in theoptical element for the optical pickup device written in item 99 or 100,in the optical function area adjoining the outside of the opticalfunction area including the optical axis in 3 optical function areas,the superposition type diffractive structure is formed, and when thesuperposition type diffractive structure gives the equivalent opticalaction to the light flux of the first wavelength λ1 and the light fluxof the second wavelength λ2, and gives the optical action different fromthe above-described optical action to the light flux of the thirdwavelength λ3, the light flux of the wavelength λ3 transmitted thesuperposition type diffractive structure is made a flare component whichdoes not contribute to the spot formation onto the information recordingsurface of the third optical information recording medium.

The invention written in item 102 is characterized in that: in theoptical element for the optical pickup device written in any one of item99 to 101, in the most outside optical function area in 3 opticalfunction areas, the superposition type diffractive structure is formed,and the diffraction efficiency η2 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the second wavelength λ2 enters into thesuperposition type diffractive structure is not larger than 40%, and thediffraction efficiency η3 of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the third wavelength λ3 enters into the superposition typediffractive structure is not larger than 40%.

The invention written in item 103 is characterized in that: in theoptical element for the optical pickup device written in any one of item99 to 102, in the most outside optical function area in 3 opticalfunction areas, the superposition type diffractive structure is formed,and when the superposition type diffractive structure gives the opticalaction different from the optical action given to the light flux of thefirst wavelength λ1 to the light flux of the second wavelength λ2 andthe light flux of the third wavelength λ3, the light fluxes of thesecond wavelength λ2 and the third wavelength λ3, which transmitted thesuperposition type diffractive structure, are respectively made flarecomponents which does not contribute to the spot formation onto theinformation recording surfaces of the second optical informationrecording medium and the third optical information recording medium.

The invention written in item 104 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 94, the thickness t1 of the protective layer of the firstoptical information recording medium and the thickness t2 of theprotective layer of the second optical information recording mediumsatisfy the following expression (77).

t1/t2≦0.4  (77)

The invention written in item 105 is characterized in that: in theoptical element for the optical pickup device written in item 104, theplurality of optical function areas are 3 optical function areas, andthe light flux of the first wavelength λ1 to the light flux of the thirdwavelength λ3 which are incident on the optical function area includingthe optical axis, in 3 optical function areas, respectively form goodwave-fronts on the information recording surfaces of the first opticalinformation recording medium to the third optical information recordingmedium, and in 3 optical function areas, the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2 which areincident on the optical function area adjoining the outside of theoptical function area including the optical axis, respectively form goodwave-front on the information recording surfaces of the first opticalinformation recording medium and the second optical informationrecording medium, and the light flux of the first wavelength λ1 incidenton the most outside optical function area in 3 optical function areas,forms a good wave-front on the information recording surface of thefirst optical information recording medium.

The invention written in item 106 is characterized in that: in theoptical element for the optical pickup device written in item 105, thesuperposition type diffractive structure is formed in the opticalfunction area adjoining the outside of the optical function areaincluding the optical axis, and the diffraction efficiency η3 of thediffracted light ray having the maximum diffraction efficiency in thediffracted light ray generated when the light flux of the thirdwavelength λ3 enters into the superposition type diffractive structure,is not larger than 40%.

The invention written in item 107 is characterized in that: in theoptical element for the optical pickup device written in item 105 or106, the superposition type diffractive structure is formed in theoptical function area adjoining the outside of the optical function areaincluding the optical axis in 3 optical function areas, and when thesuperposition type diffractive structure gives the equivalent opticalaction to the light flux of the first wavelength λ1 and the light fluxof the second wavelength λ2, and gives the optical action different fromthe above-described optical action to the light flux of the thirdwavelength λ3, the light flux of the third wavelength λ3 transmitted thesuperposition type diffractive structure is made a flare component whichdoes not contribute to the spot formation onto the information recordingsurface of the third optical information recording medium.

The invention written in item 107 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 105 to 107, the superposition type diffractive structure is formedin the most outside optical function area in 3 optical function areas,and the diffraction efficiency λ2 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the second wavelength λ2 enters into thesuperposition type diffractive structure, is not larger than 40%, andthe diffraction efficiency λ3 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the third wavelength λ3 enters into thesuperposition type diffractive structure, is not larger than 40%.

The invention written in item 109 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 105 to 108, in the most outside optical function area in 3 opticalfunction areas, the superposition type diffractive structure is formed,and when the superposition type diffractive structure gives the opticalaction different from the optical action given to the light flux of thefirst wavelength λ1 to the light flux of the second wavelength λ2 andthe light flux of the third wavelength λ3, the light fluxes of thesecond wavelength λ2 and the third wavelength λ3, which transmitted thesuperposition type diffractive structure, are respectively made flarecomponents which do not contribute to the spot formation onto theinformation recording surfaces of the second optical informationrecording medium and the third optical information recording medium.

The invention written in item 110 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 109, the paraxial power P1 (mm⁻¹) of the aberrationcorrecting element to the first wavelength λ1 and the paraxial power P2(mm⁻¹) of the light converging element to the first wavelength λ1satisfy the following expression (78).

|P1/P2|≦0.2  (78)

The invention written in item 111 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 110, the aberration correcting element is a plastic lens.

The invention written in item 112 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 111, the light converging element is a plastic lens.

The invention written in item 113 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 111, the light converging element is a glass lens.

The invention written in item 114 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 111, the light converging element is molded by using thematerial in which particles whose diameter is not larger than 30 nm aredispersed in the plastic material.

The invention written in item 115 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 114, the light converging element is corrected so that theaberration is not larger than Mareshal limit to the first wavelength λ1and the thickness t1 of the protective layer of the first opticalinformation recording medium.

According to the invention written in item 82, when the optical functionsurface of the aberration correcting element is divided into a pluralityof optical function areas around the optical axis, and the superpositiontype diffractive structure is formed in a specific optical functionarea, because it becomes possible that only one of 3 wavelengths isselectively diffracted, and the other wavelengths are not diffracted andpassed as they are, when the arrangement of each ring-shaped zone of thesuperposition type diffractive structure is adequately set, while thespherical aberration generated due to the difference of the protectivelayer thickness among 3 kinds of optical disks such as the high densityoptical disk, DVD, and CD is corrected, the high transmission factor(diffraction efficiency) can be secured to all of 3 wavelengths.Further, when the diffraction order of 3 wavelengths is made different,the degree of freedom of the optical design is spread, and a role ofdichroic filter by which the diffraction efficiency is extremely reducedto a specific wavelength, the specific wavelength is cut off, and theother wavelengths are passed, can be charged on it. Because the specificgravity of the plastic lens is smaller than the glass lens, a load onthe actuator to drive the objective optical system can be lightened, andthe follow of the objective optical system can be conducted at highspeed. Further, the plastic lens produced by the injection molding canbe mass-produced with a stable quality at the high accuracy when adesired metallic mold is accurately made. However, in the case where NAof the objective optical system is increased, when such an objectiveoptical system is a plastic lens, the influence of the refractive indexchange following the temperature change becomes large. This is for thereason that the spherical aberration generated by the refractive indexchange is increased in proportion to the fourth power of NA.

Accordingly, in the present invention, when the paraxial power P1 of theaberration correcting element to the wavelength λ1 is made positive, thelight flux of the wavelength λ1 is made incident on the light convergingelement as the converging light flux. Generally, NA∞ (hereinafter,called converted NA) which is converted into the infinite light fluxincidence for the light converging element of the finite conjugate type(magnification m≠0) of the numerical aperture NA, can be expressed byNA∞=NA (1-m). Accordingly, in the light converging element on which theconverging light flux enters, and whose magnification m>0, because theconverted NA can be reduced, the spherical aberration change generatedin the light converging element following the temperature change can besuppressed small.

Further, when the refractive power to the incident light flux is whollygiven to the light converging element arranged on the optical disk side,the working distance to CD whose protective layer thickness is maximumin 3 kinds of optical disks whose standard is different, can be securedenough.

Further, because a structure having the minute stepped section such asthe superposition type diffractive structure or optical path differencegrant structure is formed on the optical function surface of theaberration correcting element, the track is cut off by the steppedsection portion, and a rate of the light flux which does not contributeto the formation of the light converging spot, can be suppressed, andthe lowering of the transmission factor can be prevented.

In order to more effectively suppress the spherical aberration generatedin the light converging element following the temperature change small,as in the invention written in item 83, it is preferable that theaberration correcting element is made a plastic lens, and the paraxialrefractive power PR of the aberration correcting element to thewavelength λ1 is made positive. Because, in the plastic lens, when thetemperature rises, the refractive index is lowered, when the aberrationcorrecting element is a positive lens, the degree of convergence of theincident light flux on the light converging element becomes small.Because this is equivalent to the case where the magnification m of thelight converging element is reduced, by this magnification change, thespherical aberration changes toward the under correction direction. Onthe one hand, in the light converging element, when the temperaturerises, because the spherical aberration changes toward the overcorrection direction, it can cancel with the spherical aberration changeby the magnification change.

According to the invention of item 84, when the superposition typediffractive structure is formed in a optical function area including theoptical axis, because it becomes possible that only one of 3 wavelengthsis selectively diffracted, and the other wavelengths are not diffractedand passed as they are, when the arrangement of each ring-shaped zone ofthe superposition type diffractive structure is adequately set, thespherical aberration generated due to the difference of the protectivelayer thickness between the high density optical disk and DVD, or thespherical aberration generated due to the difference of the protectivelayer thickness between DVD and CD, can be corrected.

Hereupon, as the stepped section amount Δ of the superposition typediffractive structure, and the number of stepped sections, combinationsin tables 1-8, which will be described later, are preferable.

When the superposition type diffractive structure is formed in a commonoptical function area of the light fluxes of 3 wavelengths used forforming the spot on the information recording surfaces of 3 opticaldisks, as in the invention of item 85, it is preferable that the depth Δof the stepped section, and optical path difference addition amountsφ1-φ3 to each wavelength of the wavelengths λ1-λ3 for one pitchstructured by N stepped sections are set so as to satisfy theexpressions (54)-(59). Hereby, the high transmission factor (diffractionefficiency) can be secured to all of 3 wavelengths.

Further, when φ1 becomes too large, because the depth of one steppedsection is increased, as a result, the depth Δ(N+1) for one pitch isincreased, further, when the stepped section N becomes too many, thewidth of the stepped section for one pitch becomes small. Hereby,problems that the processing of the metallic mold is difficult, andvariation of the transmission factor (diffraction efficiency) to theminute wavelength change of the incident light flux becomes large, areactualized. In order to prevent the actualization of these problems, asin the invention of item 86, it is preferable that the optical pathdifference addition amount φ1 for one pitch to the wavelength λ1, andthe number N of the stepped sections formed in each ring-shaped zone aremade so as to satisfy the expressions (60), (61).

In order to effectively correct the spherical aberration generated dueto the difference of the protective layer thickness of the high densityoptical disk and DVD, or the spherical aberration generated due to theprotective layer thickness of DVD and CD by the superposition typediffractive structure, as in the invention of item 87, it is preferablethat, by the superposition type diffractive structure, the depth Δ ofthe stepped section of the superposition type diffractive structure, andthe optical difference addition amounts φ1-φ3 to each wavelength of thewavelengths λ1-λ3 for one pitch structured by N stepped sections aredetermined so that the equivalent optical action is given to thewavelength λ1 and the wavelength λ3, and to the wavelength λ2, theoptical action different from this, is given.

Hereby, it becomes possible that, while the magnification m1 to the highdensity optical disk and the magnification m2 to DVD are made almost thesame, the spherical aberration generated due to the difference of theprotective layer thickness between the high density optical disk and DVDis corrected, or while the magnification m2 to DVD and the magnificationm3 to CD are made almost the same, the spherical aberration generateddue to the difference of the protective layer thickness between DVD andCD is corrected.

Specifically, as in the invention written in item 88, a structure bywhich, when, to wavelength λ1 and wavelength λ3, practically the opticalpath difference is not given between adjoining ring-shaped zones(0-degree diffraction), and to the wavelength λ2, the optical pathdifference is given between adjoining ring-shaped zones, 1-degreediffracted light ray is generated, is preferable.

More specifically, as in the invention written in item 89, it ispreferable that, when the aberration correcting element is formed of thematerial in which the refractive index to the wavelength λ1 is withinthe range of 1.5-1.6, and Abbe's number on d-line is within the range of50-60, it is preferable that the number N of the stepped sections formedin each ring-shaped zone, and the depth D=Δ(n+1) for one pitchstructured by N stepped sections are set so as to satisfy any one of theexpressions (65)-(68).

Hereupon, expressions (65)-(68) which are preferable combinations of thenumber N of the stepped sections formed in each ring-shaped zone and thedepth D for one pitch structured by N-stepped sections, have arelationship in which the Table 1, which will be described later,corresponds to the expression (65), Table 2 corresponds to expression(66), Table 3 corresponds to expression (67), and Table 4 corresponds toexpression (68).

Hereby, to the wavelength λ1 and the wavelength λ3, 0-degree diffractedlight ray which does not practically give the optical path differencebetween adjoining ring-shaped zones, and to the wavelength λ2, 1-degreediffracted light ray can be generated when it gives the optical pathdifference between adjoining ring-shaped zones, and the hightransmission factor (diffraction efficiency) can be secured to all ofwavelengths λ1-λ3.

Further, the superposition type diffractive structure may also be made,as in the invention of item 90, a structure in which, to the wavelengthλ1 and the wavelength λ3, when it is made practically not to give theoptical path difference between adjoining ring-shaped zones (0-degreediffractive structure), and to the wavelength λ2, it gives the opticalpath difference between adjoining ring-shaped zones, 2nd-degreediffracted light ray is generated.

In this case, as in the invention of item 91, it is preferable that thenumber N of the stepped sections formed in each ring-shaped zone, andthe depth D=Δ(N+1) for one pitch structured by N stepped sections, areset so as to satisfy any one of expressions (72)-(75).

Hereby, to the wavelength λ1 and wavelength λ3, 0-degree diffractedlight ray which practically does not give the optical path differencebetween adjoining ring-shaped zones, and when, to the wavelength λ2, theoptical path difference is given between adjoining ring-shaped zones,2nd-degree diffracted light ray can be generated, and the hightransmission factor (diffraction efficiency) can be secured to all ofthe wavelengths λ1-λ3. Hereupon, Table 5, which will be described later,corresponds to the expression (72), Table 6 corresponds to theexpression (73), Table 7 corresponds to the expression (74), and Table 8corresponds to the expression (75).

Further, as in the invention of item 92, the superposition typediffractive structure may be formed in not only the optical functionarea including the optical axis, but in all of optical function areas.

Alternatively, as in the invention of item 93, corresponding to thefunction given to the superposition type diffractive structure, thesuperposition type diffractive structure is formed only in necessaryoptical function area, and there may also be the optical function areain which the superposition type diffractive structure is not formed.

Further, as in the invention of item 94, the superposition typediffractive structure may also be formed in a plurality of opticalfunction areas of the aberration correcting element, and in this case,because the width of each stepped section formed in each ring-shapedzone can be widened, the metallic mold processing by SPDT becomes easy,further, there is an advantage in which, to the wavelength λ1 of theblue violet range, the lowering of the diffraction efficiency by theshape error of the metallic mold is not too large.

As in the invention of item 95, the optical element having thesuperposition type diffractive structure of the present invention can beapplied also to the optical pickup device by which therecording/reproducing of the information is conducted by the objectiveoptical system of NA 0.65, and which has the interchangeability with thehigh density optical disk, DVD and CD of a standard in which theprotective layer thickness is about 0.6 mm.

In such a case, as in the invention of item 96, when the effectivediameter of the aberration correcting element to the wavelength λ1 andthe effective diameter to the wavelength λ2 are the same, it ispreferable that the optical function surface of the aberrationcorrecting element is divided into 2 optical function areas of theoptical function area including the optical axis corresponding to thatwithin the effective diameter to the wavelength λ3, and the opticalfunction area surrounding its periphery.

Then, as in the invention of item 97, it is preferable that thesuperposition type diffractive structure is formed in the opticalfunction area corresponding to that from the effective diameter to thewavelength λ3 to the effective diameter to the wavelengths λ1 and λ2,and the number N of the stepped sections formed in each ring-shaped zoneof this superposition type diffractive structure, and the depth D forone pitch structured by N stepped sections are adequately set, and arole of a dichroic filter by which the light fluxes of the wavelength λ1and the wavelength λ2 are transmitted with the high transmission factor(diffraction efficiency), and the diffraction efficiency to the lightflux of the wavelength λ3 is extremely reduced, is given to it.

Hereby, because the aperture limit to CD is automatically conducted, thesimple structured optical element for which the aperture limit elementof another member is not necessary, can be provided.

As an example of such a superposition type diffractive structure, astructure in Tables 11-13, which will be described later, can be listed.

When, in this manner, to the superposition type diffractive structureformed in the optical function area corresponding to that from theeffective diameter to the wavelength λ3 to the effective diameter to thewavelengths λ1 and λ2, the aperture limit function is given, as in theinvention of item 98, it is preferable that a structure by which theequivalent optical action is given to the light fluxes of the wavelengthλ1 and the wavelength λ2, and to the wavelength λ3, the optical actiondifferent from this is given, is applied, and the light flux of thewavelength λ3 transmitted the superposition type diffractive structureis made a flare component which does not contribute to the spotformation onto the information recording surface of CD.

A specific example of such a superposition type diffractive structure isa structure in Table 11 by which, to the light fluxes of wavelengths λ1and λ2, the optical path difference is not practically given, and onlythe light flux of the wavelength λ3 is diffracted toward ±2nd-degreedirection.

On the one hand, when the effective diameter to the wavelength λ1 of theaberration correcting element, and the effective diameter to thewavelength λ2 are different, as in the invention of item 99, it ispreferable that the optical function surface of the aberrationcorrecting element is divided into 3 optical function areas of theoptical function area including the optical axis corresponding to thatwithin the effective diameter to the wavelength λ3, and the opticalfunction area corresponding to the effective diameter from the effectivediameter to the wavelength λ3 surrounding its periphery to the effectivediameter to the wavelength λ2, and further, the optical function areacorresponding to that from the effective diameter to the wavelength λ2surrounding its periphery to the effective diameter to the wavelengthλ1.

Then, as in the invention of item 100, in the optical function areacorresponding to that from the effective diameter to the wavelength λ3to the effective diameter to the wavelength λ2, the superposition typediffractive structure is formed, and the number N of the steppedsections formed in each ring-shaped zone of this superposition typediffractive structure, and the depth D for one pitch structured byN-stepped sections are adequately set, and the light fluxes of thewavelength λ1 and the wavelength λ2 are transmitted with the hightransmission factor (diffraction efficiency), and the diffractionefficiency to the light flux of the wavelength λ3 is extremely reduced,and it is preferable that a role of dichroic filter is given to it.

Hereby, because the aperture limit to CD is automatically conducted, asimple-structured optical element for which the aperture limit elementof another member is not necessary, can be provided.

As an example of such a superposition type diffractive structure, astructure as in Tables 11-13, which will be described later, is listed.

As described above, when the aperture limit function is given to thesuperposition type diffractive structure formed in the optical functionarea corresponding to the effective diameter from the effective diameterto the wavelength λ3 to the effective diameter to the wavelength λ2, asin the invention of item 101, it is preferable that a structure isapplied in which the equivalent optical action is given to the lightfluxes of the wavelength λ1 and the wavelength λ2, and to the light fluxof the wavelength λ3, the optical action different from this, is given,and the light flux of the wavelength λ3 transmitted the superpositiontype diffractive structure is made a flare component which does notcontribute to the spot formation onto the information recording surfaceof CD.

A specific example of such a superposition type diffractive structure isa structure in Table 11 by which the optical path difference is notpractically given to light fluxes of wavelengths λ1 and λ2, and only thelight flux of the wavelength λ3 is diffracted toward ±2nd-degreedirection.

Further, as in the invention of item 102, the superposition typediffractive structure is formed in the optical function areacorresponding to that from the effective diameter to the wavelength λ2to the effective diameter to the wavelength λ1, and the number N of thestepped sections formed in each ring-shaped zone of this superpositiontype diffractive structure, and the depth D for one pitch structured byN-stepped sections are adequately set, and the light flux of thewavelength λ1 is transmitted with the high transmission factor(diffraction efficiency), and the diffraction efficiency to the lightfluxes of the wavelengths λ2 and λ3 is extremely reduced, and it ispreferable that a role of dichroic filter is given to it.

Hereby, because the aperture limit to CD and DVD is automaticallyconducted, a simple-structured optical element for which the aperturelimit element of another member is not necessary, can be provided.

As described above, when the aperture limit function is given to thesuperposition type diffractive structure formed in the optical functionarea corresponding to that from the effective diameter to the wavelengthλ2 to the effective diameter to the wavelength λ1, as in the inventionof item 103, a structure is applied in which the optical actiondifferent from the light flux of the wavelength λ1 is given to the lightfluxes of the wavelength λ2 and the wavelength λ3, and it is preferablethat the light fluxes of the wavelengths λ2 and λ3 transmitted thesuperposition type diffractive structure are made the flare componentwhich does not contribute to the spot formation onto the informationrecording surfaces of DVD and CD.

A specific example of such a superposition type diffractive structure isa structure in Table 14 by which the optical path difference is notpractically given to light flux of wavelength λ1, and the light flux ofthe wavelength λ2 is diffracted toward −2nd-degree direction, and thelight flux of the wavelength λ3 is diffracted toward ±3rd-degreedirection.

Hereupon, in the inventions from the item 99 to 103, a case where theeffective diameter to the wavelength λ1 is larger than the effectivediameter to the wavelength λ2, is taken as an example and the effect isdescribed, however, also to a case where the effective diameter to thewavelength λ2 is larger than the effective diameter to the wavelengthλ1, the same effect can be given.

As in the invention of item 104, the optical element having thesuperposition type diffractive structure of the present invention can beapplied also to the optical pickup device having the interchangeabilityto the high density optical disk (for example, blue ray disk) of thestandard in which the recording/reproducing of the information isconducted by the objective optical system of NA 0.85, and the thicknessof the protective layer is about 0.1 mm, and DVD and CD.

In such a case, as in the invention of item 105, it is preferable thatthe optical function surface of the aberration correcting element isdivided into 3 optical function areas of the optical function areaincluding the optical axis corresponding to that within the effectivediameter to the wavelength λ3, optical function area corresponding tothe effective diameter from the effective diameter to the wavelength λ3surrounding its periphery to the effective diameter to the wavelengthλ2, and further, the optical function area corresponding to theeffective diameter from the effective diameter to the wavelength λ2surrounding its periphery to the effective diameter to the wavelengthλ1.

Then, as in the invention of item 106, it is preferable that, in theoptical function area corresponding to the effective diameter from theeffective diameter to the wavelength λ3 to the effective diameter to thewavelength λ2, the superposition type diffractive structure is formed,and the number N of stepped sections formed in each ring-shaped zone ofthis superposition type diffractive structure, and the depth D for onepitch structured by N stepped sections are adequately set, and the lightfluxes of the wavelength λ1 and the wavelength λ2 are transmitted withthe high transmission factor (diffraction efficiency), the diffractionefficiency to the light flux of the wavelength λ3 is extremely reduced,and a role of the dichroic filter is given to it.

Hereby, because the aperture limit to CD is automatically conducted, asimple-structured optical element for which the aperture limit elementof another member is not necessary, can be provided.

As an example of such a superposition type diffractive structure, astructure as in Tables 11-13, which will be described later, is listed.

As described above, when the aperture limit function is given to thesuperposition type diffractive structure formed in the optical functionarea corresponding to the effective diameter from the effective diameterto the wavelength λ3 to the effective diameter to the wavelength λ2, asin the invention of item 107, it is preferable that a structure isapplied in which the equivalent optical action is given to the lightfluxes of the wavelength λ1 and the wavelength λ2, and to the light fluxof the wavelength λ3, the optical action different from this, is given,and the light flux of the wavelength λ3 transmitted the superpositiontype diffractive structure is made a flare component which does notcontribute to the spot formation onto the information recording surfaceof CD.

A specific example of such a superposition type diffractive structure isa structure in Table 11 by which the optical path difference is notpractically given to light fluxes of wavelengths λ1 and λ2, and only thelight flux of the wavelength λ3 is diffracted toward ±2nd-degreedirection.

Further, as in the invention of item 108, it is preferable that, in theoptical function area corresponding to the effective diameter from theeffective diameter to the wavelength λ2 to the effective diameter to thewavelength λ1, the superposition type diffractive structure is formed,and the number N of stepped sections formed in each ring-shaped zone ofthis superposition type diffractive structure, and the depth D for onepitch structured by N stepped sections are adequately set, and the lightflux of the wavelength λ1 is transmitted with the high transmissionfactor (diffraction efficiency), the diffraction efficiency to lightfluxes of the wavelengths λ2 and λ3 is extremely reduced, and a role ofthe dichroic filter is given to it.

Hereby, because the aperture limit to CD and DVD is automaticallyconducted, a simple-structured optical element for which the aperturelimit element of another member is not necessary, can be provided.

As described above, when the aperture limit function is given to thesuperposition type diffractive structure formed in the optical functionarea corresponding to the effective diameter from the effective diameterto the wavelength λ2 to the effective diameter to the wavelength λ1, asin the invention of item 109, it is preferable that a structure isapplied in which the optical action different from the light flux of thewavelength λ1 is given to the light fluxes of the wavelength λ2 and thewavelength λ3, and the light fluxes of the wavelengths λ2 and λ3transmitted the superposition type diffractive structure are made aflare component which does not contribute to the spot formation onto theinformation recording surfaces of DVD and CD.

A specific example of such a superposition type diffractive structure isa structure in Table 14 by which the optical path difference is notpractically given to light fluxes of wavelengths λ1, the light flux ofthe wavelength λ2 is diffracted toward the −2nd-degree direction, andthe light flux of the wavelength λ3 is diffracted toward ±3rd-degreedirection.

Further, as in the invention of item 110, it is preferable that theparaxial power P1 of the aberration correcting element to the wavelengthλ1 and the paraxial power P2 of the light converging element are set soas to satisfy the expression (78).

Hereby, because the refractive power to the incident light flux can bewholly given to the light converging element arranged on optical diskside, the working distance to CD whose protective layer thickness is themaximum in 3 kinds of optical disks whose standard is different, can besecured enough.

Further, by the stepped section portion of the superposition typediffractive structure, diffractive structure, or optical path differencegrant structure, the track is cut off, and a rate of the light fluxwhich does not contribute to the formation of light converging spot, canbe suppressed, and the lowering of the transmission factor can beprevented.

As in the invention of item 111, when the aberration correcting elementis a plastic lens, it is preferable because the transfer property whenthe minute structure such as the superposition type diffractivestructure, diffractive structure, or optical path difference grantstructure, is molded, can be increased.

As in the invention of item 112, when the light converging element ismade a plastic lens, the mass-production can be high accuratelyconducted with the stable quality. Hereupon, when the light convergingoptical element having the large light converging power is made aplastic lens, although the influence of the refractive index changefollowing the temperature change becomes large, when the aberrationcorrecting element used in combination with this is made a structure asin items 64, 76, 81, the spherical aberration by the refractive indexchange can be effectively suppressed.

On the one hand, as in the invention of item 113, when the lightconverging optical element is made a glass lens, it can be made a lightconverging element having the high reliability for the light resistanceto the light in the blue violet region, temperature resistance, andtransmission factor.

When, as a glass lens, the glass material whose glass transition pointTg is not larger than 400° C., is used, because the molding at acomparatively low temperature, becomes possible, the life of themetallic mold can be prolonged. Hereby, the production cost of the lightconverging element can be lowered.

As such a glass material whose transition point Tg is low, for example,there is K-PG325 or K-PG375 (both are trade names) of (Co.) SumitaGlass.

Further, as a material of the light converging element, as in theinvention of item 114, a material for which, in the plastic material,particles whose diameter is not larger than 30 nm, are dispersed, mayalso be used.

When, in a plastic material in which, when the temperature rises, therefractive index is reduced, the inorganic material in which, when thetemperature rises, the refractive index is increased, is homogeneouslymixed, the temperature dependency of the refractive index of both, canbe cancelled. Hereby, while the molding property of the plastic materialis maintained, the optical material in which the refractive index changefollowing the temperature change is small, (hereinafter, such an opticalmaterial is called “a-thermal resin”), can be used.

Herein, the temperature change of the refractive index of the lightconverging element will be described. The changing rate of therefractive index to the temperature change is, according to the formulaof Lorentz-Lorenz, when the refractive index n is differentiated by thetemperature t, expressed by A shown by the following Arith. 2.

$\begin{matrix}{A = {\frac{( {n^{2} + 2} )( {n^{2} - 1} )}{6n}\{ {( {{- 3}\alpha} ) + {\frac{1}{\lbrack R\rbrack}\frac{\delta \lbrack R\rbrack}{\delta \; t}}} \}}} & ( {{Arith}.\mspace{11mu} 2} )\end{matrix}$

Where, n is the refractive index of the light converging lens to thewavelength of the laser light source, α is a line expansion coefficient,and [R] is a molecular refractive power of the light converging element.

In the case of a general plastic material, because the contribution ofthe term 2 is smaller than that of the term 1, the term 2 can be almostneglected. For example, in the case of acrylic resin (PMMA), linearexpansion coefficient α is 7×10⁻⁵, and when it is substituted into theabove-expression, A=−12×10⁻⁵, and generally it is equal to the measuredvalue.

Herein, in the light converging element in the present invention, whenthe inorganic material is dispersed into minute particle plasticmaterial whose diameter is not larger than 30 nm, the contribution ofthe term 2 is practically increased, and is made to cancel out with thechange by the linear expansion of the term 1.

Specifically, it is preferable that the refractive index changing rateto the temperature change, which is, conventionally, about −12×10⁻⁵, issuppressed to fewer than 10×10⁻⁵ in the absolute value. More preferably,it is preferable to suppress it fewer than 8×10⁻⁵, further preferably,fewer than 6×10⁻⁵, for the reduction of the spherical aberration changefollowing the temperature change of the light converging element.

For example, when the minute particles of niobium oxide (Nb₂O₅) aredispersed in acrylic resin (PMMA), such a dependency of the refractiveindex change to the temperature change can be dissolved.

The plastic material which is a base material, is 8.0 in a volume ratio,and niobium oxide is a rate of about 2.0, and these are uniformly mixed.Although there is a problem that the minute particles are easilycoagulated, a technology by which the electric charge is given onto theparticle surface, and particles are dispersed, is also well known, andnecessary dispersion condition can be generated.

Hereupon, this volume ratio can be appropriately increased or decreasedto control the rate of the change of the refractive index to thetemperature change, and a plurality of kinds of nano-size inorganicparticle are blended, and can be dispersed.

Although, in the volume ratio, in above example, it is 80:20, it can beappropriately adjusted within the range from 90:10-to 60:40. When thevolume ratio is smaller than 90:10, the effect of the refractive indexchange suppression is reduced, inversely, when it exceeds 60:40, it isnot preferable because a problem is generated in the molding property ofa-thermal resin.

It is preferable that a particle is an inorganic substance, and further,it is preferable that it is an oxide. Then, it is preferable that theoxide condition is saturated, and it is an oxide which is not moreoxidized.

A fact that it is an oxide, is preferable for suppressing low thereaction to the plastic material which is a high polymer organiccompound, and further, by a fact that it is an oxide, the transmissionfactor deterioration or wave-front aberration deterioration followingthe irradiation of a long period of time of the blue violet laser can beprevented. Particularly, under the severe condition that the blue violetlaser is irradiated under the high temperature, the oxidation is easilyaccelerated, however, when it is such an inorganic oxide, thetransmission factor deterioration or wave-front aberration deteriorationby the oxidation can be prevented.

Hereupon, when the diameter of the particle dispersed in the plasticmaterial is large, the scattering of the incident light flux is easilygenerated, and the transmission factor of the light converging elementis lowered. In the high density optical disk, in the blue violet laserused for the recording/reproducing of the information, because the laserpower by which a stable laser oscillation can be obtained for a longperiod of time, is about 30 mW, when the transmission factor of theoptical element to the blue violet laser is low, it is disadvantageousin the point of view of the speeding up of the recording of theinformation, and multi-layer disk correspondence. Accordingly, it ispreferable for preventing the lowering of the transmission factor of thelight converging element that the diameter of the particle dispersed inthe plastic material is preferably not larger than 20 nm, morepreferably, not larger than 10-15 nm.

Generally, in the optical element, the shorter the wavelength is, andthe larger NA is, its production is more difficult. Accordingly, as inthe invention of item 115, it is preferable that the aberrationcorrection of the light converging element is made to be optimized tothe wavelength λ1 of the high density optical disk and the thickness t1of the protective layer, and when it is combined with the aberrationcorrecting element, the performance as the optical element for the highdensity optical disk can be easily exerted.

The invention written in item 116 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; and the optical pickup device hasan objective optical system for respectively light-converging the lightfluxes of the first wavelength λ1 to third wavelength λ3 onto recordingsurfaces of the first optical information recording medium to the thirdoptical information recording medium; and as the objective opticalsystem, the optical element written in any one of items 45 to 115 isused.

The invention written in item 117 is characterized in that: the opticalpickup device written in item 116 is mounted, and at least one of therecording of the information for the first optical information recordingmedium to the third optical information recording medium, and thereproducing of the information for the first optical informationrecording medium to the third optical information recording medium, canbe conducted.

The invention written in item 118 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; and in the optical function surfaces ofthe aberration correcting element, at least one optical function surfaceis divided into a plurality of ring-shaped zone-like optical functionareas around the optical axis; and in at least one optical function areain the plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of ring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed.

The invention written in item 119 is characterized in that: in theaberration correcting element for the optical pickup device written initem 118, the optical function area in which the superposition typediffractive structure is formed, is an optical function area includingthe optical axis, and the paraxial diffraction power of thesuperposition type diffractive structure to the second wavelength λ2 isnegative.

The invention written in item 120 is characterized in that: in theaberration correcting element for the optical pickup device written initem 118 or 119, the optical function area in which the superpositiontype diffractive structure is formed, is an optical function areaincluding the optical axis, and the superposition type diffractivestructure adds the under-correction spherical aberration to the secondwavelength λ2.

The invention written in item 121 is characterized in that: in theaberration correcting element for the optical pickup device written initem 118, the optical function area in which the superposition typediffractive structure is formed, is an optical function area includingthe optical axis, and the paraxial diffraction power of thesuperposition type diffractive structure to the second wavelength λ2 ispositive.

The invention written in item 122 is characterized in that: in theaberration correcting element for the optical pickup device written initem 118 or 121, the optical function area in which the superpositiontype diffractive structure is formed, is an optical function areaincluding the optical axis, and the superposition type diffractivestructure adds the over-correction spherical aberration to the secondwavelength λ2.

The invention written in item 123 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; in the optical function surfaces of theaberration correcting element, at least one optical function surface isdivided into a plurality of ring-shaped zone-like optical function areasaround the optical axis; in the optical function area including theoptical axis in the plurality of ring-shaped zone-like optical functionareas, the superposition type diffractive structure which is a structurein which a plurality of ring-shaped zones inside of which apredetermined number of discontinuous stepped sections are formed, arecontinuously arranged around the optical axis, is formed; and the firstlight flux λ1, and in the superposition type diffractive structure, inthe discontinuous stepped sections formed in each ring-shaped zone, theminimum value P of the interval in the perpendicular direction to theoptical axis between adjoining stepped sections satisfy the followingexpressions (79) and (80).

0.39 μm<λ1<0.42 μm  (79)

P>3 μm  (80)

The invention written in item 124 is characterized in that: in theaberration correcting element for the optical pickup device written initem 123, in the superposition type diffractive structure, the minimumvalue P of the interval in the direction perpendicular to the opticalaxis between adjoining stepped sections in the discontinuous steppedsection formed in each ring-shaped zone, satisfies the followingexpression (81).

P>5 μm

The invention written in item 125 is characterized in that: in theaberration correcting element for the optical pickup device written initem 124, in the superposition type diffractive structure, the minimumvalue P of the interval in the direction perpendicular to the opticalaxis between adjoining stepped sections in the discontinuous steppedsection formed in each ring-shaped zone, satisfies the followingexpression (82).

P>10 μm  (82)

The invention written in item 126 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; in the optical function surfaces of theaberration correcting element, at least one optical function surface isdivided into a plurality of ring-shaped zone-like optical function areasaround the optical axis; in the optical function area including theoptical axis in the plurality of ring-shaped zone-like optical functionareas, the superposition type diffractive structure which is a structurein which a plurality of ring-shaped zones inside of which apredetermined number of discontinuous stepped sections are formed, arecontinuously arranged around the optical axis, is formed; and when theoptical path difference added to the transmission wave-front by thesuperposition type diffractive structure is defined by the arith-1,signs of B2 and B4 are different from each other.

The invention written in item 127 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; in the optical function surfaces of theaberration correcting element, at least one optical function surface isdivided into a plurality of ring-shaped zone-like optical function areasaround the optical axis; in at least two optical function areas in theplurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of ring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed; and in the superposition typediffractive structure, any one of the number N of the discontinuousstepped sections formed in each ring-shaped zone, and the depth Δ (μm)in the optical axis direction of the discontinuous stepped sections, isdifferent for each optical function area.

The invention written in item 128 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; in the optical function surfaces of theaberration correcting element, at least one optical function surface isdivided into a plurality of ring-shaped zone-like optical function areasaround the optical axis; in at least one optical function area in theplurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of ring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed; and the diffractive structure formedof a plurality of ring-shaped zones divided by the stepped sectionaround the optical axis, is formed.

The invention written in item 129 is characterized in that: in theaberration correcting element for the optical pickup device written initem 128, the depth of the stepped section of the diffractive structureis, to the diffraction order n1 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the first wavelength λ1 enters, the diffractionorder n2 of the diffracted light ray having the maximum diffractionefficiency in the diffracted light ray generated when the light flux ofthe second wavelength λ2 enters, and the diffraction order n3 of thediffracted light ray having the maximum diffraction efficiency in thediffracted light ray generated when the light flux of the thirdwavelength λ3 enters, are designed so that they are the lower degreewith together.

The invention written in item 130 is characterized in that: in theaberration correcting element for the optical pickup device written initem 129, the first wavelength λ1 (μm), the second wavelength λ2 (μm),the third wavelength λ3 (μm) respectively satisfy the followingexpressions (83) to (85), and the combination of the diffraction ordern1, diffraction order n2, and diffraction order n3 is any one of (n1,n2, n3)=(2, 1, 1), (4, 2, 2), (6, 4, 3,), (8, 5, 4), (10, 6, 5).

0.39<λ1<0.42  (83)

0.63<λ2<0.68  (84)

0.75<λ3<0.85  (85)

The invention written in item 131 is characterized in that: in theaberration correcting element for the optical pickup device written initem 129 or 130, the aberration correcting element is formed of amaterial whose refractive index in the first wavelength λ1 is within therange of 1.5-1.6, and Abbe's number on d-line is within the range of50-60, and the depth d1 in the optical axis direction of the steppedsection closest to the optical axis in the stepped sections of thediffractive structure, satisfies any one of the following expressions(86) to (90).

1. 2 μm>d1>1.7 μm  (86)

2. 6 μm>d1>3.0 μm  (87)

4. 4 μm<d1<5.0 μm  (88)

5. 6 μm<d1<6.5 μm  (89)

6. 9 μm>d1>8.1 μm  (90)

The invention written in item 132 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 128 to 131, the paraxial diffraction power PD0 (mm⁻¹)to the first wavelength λ1 of the diffractive structure, the paraxialdiffraction power PD1 (mm⁻¹) to the wavelength 10 nm longer than thefirst wavelength λ1 of the diffractive structure, and the paraxialdiffraction power PD2 (mm⁻¹) to the wavelength 10 nm shorter than thefirst wavelength λ1 of the diffractive structure, satisfy the followingexpression (91).

PD2<PD0<PD1  (91)

The invention written in item 133 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 128 to 132, the diffractive structure has thewavelength dependency of the spherical aberration in which, when thefirst wavelength λ1 changes toward the long wavelength side, thespherical aberration changes toward the under correction direction, andwhen the first wavelength λ1 changes toward the short wavelength side,the spherical aberration changes toward the over correction direction.

The invention written in item 134 is characterized in that: in theaberration correcting element for the optical pickup device written initem 133, in the optical function surfaces of the aberration correctingelement, at least one optical function surface is divided into thecenter optical function area and the peripheral optical function areasurrounding the periphery of the central optical function area, and onlyin the peripheral optical function area, the diffractive structure isformed.

The invention written in item 135 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 128 to 134, the sectional shape including the opticalaxis of the diffractive structure is a step shape.

The invention written in item 136 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 128 to 134, the sectional shape including the opticalaxis of the diffractive structure is a saw-toothed shape.

The invention written in item 137 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 128 to 136, the superposition type diffractivestructure is formed on one optical function surface of the aberrationcorrecting element, and the diffractive structure is formed on anotheroptical function surface.

The invention written in item 138 is characterized in that: it is anaberration correcting element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the aberration correcting element is arranged in theoptical path between the first light source to the third light source,and the light converging element by which the light flux of the firstwavelength λ1 projected from the first light source to the light flux ofthe third wavelength λ3 projected from the third light source arerespectively light converged on information recording surfaces of thefirst optical information recording medium to the third opticalinformation recording medium; in the optical function surfaces of theaberration correcting element, at least one optical function surface isdivided into a plurality of ring-shaped zone-like optical function areasaround the optical axis; in at least one optical function area in theplurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of ring-shaped zones inside of which a predetermined number ofdiscontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed; and the optical difference grantstructure formed of a plurality of ring-shaped zones divided by thestepped section is formed in the central area including the optical axisand on the outside of the central area.

The invention written in item 139 is characterized in that: in theaberration correcting element for the optical pickup device written initem 138, the optical path difference grant structure has thetemperature dependency in which, when the environmental temperaturerises, the spherical aberration added to the first wavelength λ1 changestoward the under correction direction, and when the environmentaltemperature falls, the spherical aberration added to the firstwavelength λ1 changes toward the over correction direction.

The invention written in item 140 is characterized in that: in theaberration correcting element for the optical pickup device written initem 139, in the optical path difference grant structure, thering-shaped zone adjoining the outside of the central area is formed byshifting in the optical axis direction so that the optical path lengthis short to the central area, and the ring-shaped zone in the maximumeffective diameter position is formed by shifting in the optical axisdirection so that the optical path length becomes long to thering-shaped zone adjoining its inside, and the ring-shaped zone at the75% position of the maximum effective diameter is formed by shifting inthe optical axis direction so that the optical path length becomes shortto the ring-shaped zone adjoining its inside and to the ring-shaped zoneadjoining its outside.

The invention written in item 141 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 139 to 140, by the first wavelength λ1 (μm), the secondwavelength λ2 (μm), the third wavelength λ3 (μm), the depth d2 (μm) inthe optical axis direction of the stepped section closest to the opticalaxis in stepped sections of the optical path difference grant structure,the refractive index Nλ1 to the first wavelength λ1 of the aberrationcorrecting element, the refractive index Nλ2 to the second wavelength λ2of the aberration correcting element, and the refractive index Nλ3 tothe third wavelength λ3 of the aberration correcting element, Φ1, Φ2, Φ3respectively expressed by the following expressions (92) to (94) satisfythe following expressions (95) to (98).

Φ1=d2·(Nλ1−1)/λ1  (92)

Φ2=d2·(Nλ2−1)/λ2  (93)

Φ3=d2·(Nλ3−1)/λ3  (94)

INT(Φ1)≦10  (95)

0≦|INT(Φ1)−Φ1|≦0.4  (96)

0≦|INT(Φ2)−Φ2|≦0.4  (98)

0≦|INT(Φ3)−Φ3|≦0.4  (98)

Where, INT (Φi) (i=1, 2, 3) is an integer obtained by half-adjusting Φi.

The invention written in item 142 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 138 to 141, the superposition type diffractivestructure is formed on one optical function surface of the aberrationcorrecting element, and the optical path difference grant structure isformed on another optical function surface.

The invention written in item 143 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 142, the optical function area on which thesuperposition type diffractive structure is formed, is an opticalfunction area including the optical axis.

The invention written in item 144 is characterized in that: in theaberration correcting element for the optical pickup device written initem 143, in the first wavelength λ1 (μm), second wavelength λ2 (μm),third wavelength λ3 (μm), the superposition type diffractive structureformed in the optical function area including the optical axis, by thenumber N of discontinuous stepped sections formed in each ring-shapedzone, the depth Δ (μm) in the optical axis direction of thediscontinuous stepped section, the refractive index Nλ1 to the firstwavelength λ1 of the aberration correcting element, refractive index Nλ2to the second wavelength λ2 of the aberration correcting element, andrefractive index Nλ3 to the third wavelength λ3 of the aberrationcorrecting element, φ1, φ2, φ3 respectively expressed by the followingexpressions (99) to (101) satisfy the following expressions (102) to(104).

φ1=Δ·(Nλ1−1)·(N+1)/λ1  (99)

φ2=Δ·(Nλ2−1)·(N+1)/λ2  (100)

φ3=Δ·(Nλ3−1)·(N+1)/λ3  (101)

0≦|INT(Φ1)−Φ1|≦0.4  (102)

0≦|INT(Φ2)−Φ2|≦0.4  (103)

0≦|INT(Φ3)−Φ3|≦0.4  (104)

Where, INT (φi) (i=1, 2, 3) is an integer obtained by half-adjusting φi.

The invention written in item 145 is characterized in that: in theaberration correcting element for the optical pickup device written initem 144, φ1 and the number N of discontinuous stepped sections formedin each ring-shaped zone satisfy the following expressions (105) and(106).

φ1≦24  (105)

3<N<11  (106)

The invention written in item 146 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 143 to 145, the superposition type diffractivestructure formed in the optical function area including the opticalaxis, gives the equivalent first optical action to the light flux of thefirst wavelength λ1 and the light flux of the third wavelength λ3, andto the light flux of the second wavelength λ2, gives the second opticalaction different from the first optical action.

The invention written in item 147 is characterized in that: in theaberration correcting element for the optical pickup device written initem 146, the first optical action is 0-degree diffraction by which theoptical path difference is not practically given between adjoiningring-shaped zones to the light flux of the first wavelength λ1 and thelight flux of the third wavelength λ3, and the second optical action isthe 1st-degree diffraction by which the light flux of the secondwavelength λ2 is diffracted to the 1st-degree direction.

The invention written in item 148 is characterized in that: in theaberration correcting element for the optical pickup device written initem 147, the aberration correcting element is formed of the material inwhich the refractive index in the first wavelength λ1 is within therange of 1.5-1.6, and Abbe's number on d-line is within the range of50-60, and the first wavelength λ1 (μm), second wavelength λ2 (μm), andthird wavelength λ3 (μm) respectively satisfy the following expressions(107) to (109), and in the superposition type diffractive structureformed in the optical function area including the optical axis, acombination of the number N of discontinuous stepped sections formed ineach ring-shaped zone, and the depth D (μm) in the optical axisdirection of the ring-shaped zone, is respectively any one of thefollowing expressions (110)-(113).

0.39<λ1<0.42  (107)

0.63<λ2<0.68  (108)

0.75<λ3<0.85  (109)

When N=3, 4.1≦D≦4.8  (110)

When N=4, 5.4≦D≦6.4  (111)

When N=5, 7.0≦D≦7.9  (112)

When N=6, 8.4≦D≦9.0  (113)

The invention written in item 149 is characterized in that: in theaberration correcting element for the optical pickup device written initem 146, the first optical action is 0-degree diffraction by which theoptical path difference is not practically given between adjoiningring-shaped zones to the light flux of the first wavelength λ1 and thelight flux of the third wavelength λ3, and the second optical action isthe 2nd-degree diffraction by which the light flux of the secondwavelength λ2 is diffracted to the 2nd-degree direction.

The invention written in item 150 is characterized in that: in theaberration correcting element for the optical pickup device written initem 149, the aberration correcting element is formed of the material inwhich the refractive index in the first wavelength λ1 is within therange of 1.5-1.6, and Abbe's number on d-line is within the range of50-60, and the first wavelength λ1 (μm), second wavelength λ2 (μm), andthird wavelength λ3 (μm) respectively satisfy the following expressions(114) to (116), and in the superposition type diffractive structureformed in the optical function area including the optical axis, acombination of the number N of discontinuous stepped sections formed ineach ring-shaped zone, and the depth D (μm) in the optical axisdirection of the ring-shaped zone, is respectively any one of thefollowing expressions (117)-(120).

0.39<λ1<0.42  (114)

0.63<λ2<0.68  (115)

0.75<λ3<0.85  (116)

When N=8, 11.3≦D≦12.7  (117)

When N=9, 12.8≦D≦14.1  (118)

When N=10, 14.2≦D≦15.6  (119)

When N=11, 15.7≦D≦17.2  (120)

The invention written in item 151 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 143 to 150, the superposition type diffractivestructure is formed in all of the plurality of optical function areas.

The invention written in item 152 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 150, the superposition type diffractivestructure is not formed in at least one optical function area in theplurality of optical function areas.

The invention written in item 153 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 152, the superposition type diffractivestructure is formed in the plurality of optical function areas of theaberration correcting element.

The invention written in item 154 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 153, the plurality of optical function areas are2 optical function areas, and the superposition type diffractivestructure is formed in the optical function area not including theoptical axis in 2 optical function areas, and the diffraction efficiencyη3 of the diffracted light ray having the maximum diffraction efficiencyin the diffracted light ray generated when the light flux of thirdwavelength λ3 enters into the superposition type diffractive structure,is not larger than 40%.

The invention written in item 155 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 154, the plurality of optical function areas are2 optical function areas, and the superposition type diffractivestructure is formed in the optical function area not including theoptical axis in 2 optical function areas, and when the superpositiontype diffractive structure gives the equivalent optical action to thelight flux of the first wavelength λ1 and the light flux of the secondwavelength λ2, and to the light flux of the third wavelength λ3, theoptical action different from the above-described optical action isgiven, the light flux of the third wavelength λ3 transmitted thesuperposition type diffractive structure is made a flare component whichdoes not contribute to the spot formation onto the information recordingsurface of the third optical information recording medium.

The invention written in item 156 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 153, the plurality of optical function areas are3 optical function areas, and the superposition type diffractivestructure is formed in the optical function area adjoining the outsideof the optical function area including the optical axis in 3 opticalfunction areas, and the diffraction efficiency η3 of the diffractedlight ray having the maximum diffraction efficiency in the diffractedlight ray generated when the light flux of third wavelength λ3 entersinto the superposition type diffractive structure, is not larger than40%.

The invention written in item 157 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 153 and 156, the plurality of optical functionareas are 3 optical function areas, and the superposition typediffractive structure is formed in the optical function area adjoiningthe outside of the optical function area including the optical axis in 3optical function areas, and the superposition type diffractive structuregives equivalent optical action to the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2, and when,to the light flux of the third wavelength λ3, the optical actiondifferent from the above-described optical action is given, the lightflux of the third wavelength λ3 transmitted the superposition typediffractive structure is made a flare component which does notcontribute to the spot formation onto the information recording surfaceof the third optical information recording medium.

The invention written in item 157 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 153 and 156, the plurality of optical functionareas are 3 optical function areas, and the superposition typediffractive structure is formed in the most outside optical functionarea in 3 optical function areas, and the diffraction efficiency η2 ofthe diffracted light ray having the maximum diffraction efficiency inthe diffracted light ray generated when the light flux of the secondwavelength λ2 enters into the superposition type diffractive structureis not larger than 40%, and the diffraction efficiency η3 of thediffracted light ray having the maximum diffraction efficiency in thediffracted light ray generated when the third wavelength λ3 enters intothe superposition type diffractive structure is not larger than 40%.

The invention written in item 159 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 153 and 156 to 158, the plurality of opticalfunction areas are 3 optical function areas, and the superposition typediffractive structure is formed in the most outside optical functionarea in 3 optical function areas, and when the superposition typediffractive structure gives the optical action different from theoptical action given to the light flux of the first wavelength λ1, tothe light flux of the second wavelength λ2 and the light flux of thethird wavelength λ3, the light fluxes of the second wavelength λ2 andthe third wavelength λ3 transmitted the superposition type diffractivestructure are made flare components which do not contribute to the spotformation onto the information recording surfaces of the second opticalinformation recording medium and the third optical information recordingmedium.

The invention written in item 160 is characterized in that: in theaberration correcting element for the optical pickup device written inany one of items 118 to 159, the aberration correcting element is aplastic lens.

The invention written in item 161 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; the optical pickup device has thelight converging element by which the light flux of the first wavelengthλ1 projected from the first light source to the light flux of the thirdwavelength λ3 projected from the third light source are respectivelylight converged on the information recording surfaces of the firstoptical information recording medium to the third optical informationrecording medium, and the aberration correcting element written in anyone of items 118 to 160 is arranged in the optical path between thefirst light source to the third light source, and the light convergingelement.

The invention written in item 162 is characterized in that: the opticalpickup device written in item 161 is mounted, and in the recording ofthe information for the first optical information recording medium tothe third optical information recording medium, and the reproducing ofthe information for the first optical information recording medium tothe third optical information recording medium, at least one can beconducted.

The invention written in item 163 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in the plurality of ring-shaped zone-likeoptical function areas, in at least one optical function area, thesuperposition type diffractive structure which is a structure in which aplurality of ring-shaped zones, inside of which a predetermined numberof discontinuous stepped sections are formed, are continuously arrangedaround the optical axis, is formed.

The invention written in item 164 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in the optical function area includingthe optical axis in the plurality of ring-shaped zone-like opticalfunction areas, the superposition type diffractive structure which is astructure in which a plurality of the ring-shaped zones are continuouslyarranged around the optical axis, inside of which a predetermined numberof discontinuous stepped sections are formed, is formed; and the firstmagnification m1 when the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium, and the second magnification m2 when the reproducing and/orrecording of the information is conducted for the second opticalinformation recording medium, are almost coincident.

The invention written in item 165 is characterized in that: in the lightconverging element for the optical pickup device written in item 164,the superposition type diffractive structure adds the under correctionspherical aberration to the second wavelength λ2.

The invention written in item 166 is characterized in that: in the lightconverging element for the optical pickup device written in item 164 or166, the first magnification m1 and the second magnification m2 satisfythe following expression (121).

m1=m2=0  (121)

The invention written in item 167 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 164 to 166, the third magnification m3 when the reproducing and/orrecording is conducted for the third optical information recordingmedium satisfies the following expression (122).

−0.25<m3<−0.10  (122)

The invention written in item 168 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 164 to 167, the first light source and the second light source area packaged light source module, and the light converging elementlight-converges the light flux of the first wavelength λ1 projected fromthe light source module onto the information recording surface of thefirst optical information recording medium, and light-converges thelight flux of the wavelength λ2 projected from the light source moduleonto the information recording surface of the second optical informationrecording medium.

The invention written in item 169 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in the optical function area includingthe optical axis in the plurality of ring-shaped zone-like opticalfunction areas, the superposition type diffractive structure which is astructure in which a plurality of the ring-shaped zones are continuouslyarranged around the optical axis, inside of which a predetermined numberof discontinuous stepped sections are formed, is formed; and the secondmagnification m2 when the reproducing and/or recording of theinformation is conducted for the second optical information recordingmedium, and the third magnification m3 when the reproducing and/orrecording of the information is conducted for the third opticalinformation recording medium, are almost coincident.

The invention written in item 170 is characterized in that: in the lightconverging element for the optical pickup device written in item 169,the superposition type diffractive structure adds the over correctionspherical aberration to the second wavelength λ2.

The invention written in item 171 is characterized in that: in the lightconverging element for the optical pickup device written in item 169 or170, the first magnification m1 when the reproducing and/or recording ofthe information is conducted to the first optical information recordingmedium satisfies the following expression (123).

m1=0  (123)

The invention written in item 172 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 169 to 171, the second magnification m2 and the thirdmagnification m3 satisfy the following expressions (124) and (125).

m2=m3  (124)

−0.25<m2<−0.10  (125)

The invention written in item 173 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 169 to 172, the second light source and the third light source area packaged light source module, and the light converging elementlight-converges the light flux of the second wavelength λ2 onto theinformation recording surface of the second optical informationrecording medium, and light-converges the light flux of the thirdwavelength λ3 onto the information recording surface of the thirdoptical information recording medium.

The invention written in item 174 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in the optical function area includingthe optical axis in the plurality of ring-shaped zone-like opticalfunction areas, the superposition type diffractive structure which is astructure in which a plurality of the ring-shaped zones are continuouslyarranged around the optical axis, inside of which a predetermined numberof discontinuous stepped sections are formed, is formed; and the firstlight flux λ1, and in the superposition type diffractive structure, inthe discontinuous stepped sections formed in each ring-shaped zone, theminimum value P of the interval in the direction perpendicular to theoptical axis between the adjoining stepped sections satisfy thefollowing expressions (126) and (127).

0.39 μm<λ1<0.42 μm  (126)

P>3 μm  (127)

The invention written in item 175 is characterized in that: in the lightconverging element for the optical pickup device written in item 174, inthe superposition type diffractive structure, in the discontinuousstepped sections formed in each ring-shaped zone, the minimum value P ofthe interval in the direction perpendicular to the optical axis betweenadjoining stepped sections satisfies the following expression (128).

P>5 μm  (128)

The invention written in item 176 is characterized in that: in the lightconverging element for the optical pickup device written in item 175, inthe superposition type diffractive structure, in the discontinuousstepped sections formed in each ring-shaped zone, the minimum value P ofthe interval in the direction perpendicular to the optical axis betweenadjoining stepped sections satisfies the following expression (129).

P>10 μm  (129)

The invention written in item 177 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in the optical function area includingthe optical axis in the plurality of ring-shaped zone-like opticalfunction areas, the superposition type diffractive structure which is astructure in which a plurality of the ring-shaped zones are continuouslyarranged around the optical axis, inside of which a predetermined numberof discontinuous stepped sections are formed, is formed; and when theoptical path difference added to the transmission wave-front by thesuperposition type diffractive structure is defined by the Arith-1,signs of B2 and B4 are different from each other.

The invention written in item 178 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 174 to 177, the first magnification m1 when the reproducing and/orrecording of the information is conducted for the first opticalinformation recording medium, the second magnification m2 when thereproducing and/or recording of the information is conducted for thesecond optical information recording medium, and the third magnificationm3 when the reproducing and/or recording of the information is conductedfor the third optical information recording medium, are different fromeach other.

The invention written in item 179 is characterized in that: in the lightconverging element for the optical pickup device written in item 178,the first magnification m1, the second magnification m2, and the thirdmagnification m3 satisfy the following expressions (130) to (132).

M1=0  (130)

−0.08<m2<−0.01  (131)

−0.25<m3<−0.10  (132)

The invention written in item 180 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in at least one optical function area inthe plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of the ring-shaped zones are continuously arranged around theoptical axis, inside of which a predetermined number of discontinuousstepped sections are formed, is formed; and in the superposition typediffractive structure, any one of the number N of the discontinuousstepped sections formed in each ring-shaped zone, and the depth Δ (μm)in the optical axis direction of the discontinuous stepped sections, isdifferent for each optical function area.

The invention written in item 181 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in at least one optical function area inthe plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of the ring-shaped zones are continuously arranged around theoptical axis, inside of which a predetermined number of discontinuousstepped sections are formed, is formed; and in at least one opticalfunction surface, in the optical function surfaces of the aberrationcorrecting element, the diffractive structure formed of a plurality ofring-shaped zones divided by the stepped section around the opticalaxis, is formed.

The invention written in item 182 is characterized in that: in the lightconverging element for the optical pickup device written in item 181,the depth of the stepped section of the diffractive structure isdesigned so that, to the diffraction order n1 of the diffracted lightray having the maximum diffraction efficiency in the diffracted lightray generated when the light flux of the first wavelength λ1 enters,both of the diffraction order n2 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the second wavelength λ2 enters, and thediffraction order n3 of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the third wavelength λ3 enters, are lower degree.

The invention written in item 183 is characterized in that: in the lightconverging element for the optical pickup device written in item 182,the first wavelength λ1 (μm), the second wavelength λ2 (μm), the thirdwavelength λ3 (μm) respectively satisfy the following expressions (133)to (135), and the combination of the diffraction order n1, diffractionorder n2, and diffraction order n3 is any one of (n1, n2, n3)=(2, 1, 1),(4, 2, 2), (6, 4, 3,), (8, 5, 4), (10, 6, 5).

0.39<λ1<0.42  (37)

0.63<λ2<0.68  (38)

0.75<λ3<0.85  (39)

The invention written in item 184 is characterized in that: in the lightconverging element for the optical pickup device written in item 182 or183, the light converging element is formed of a material whoserefractive index in the first wavelength λ1 is within the range of1.5-1.6, and Abbe's number on d-line is within the range of 50-60, andthe depth d1 in the optical axis direction of the stepped sectionclosest to the optical axis in the stepped sections of the diffractivestructure, satisfies any one of the following expressions (136) to(140).

1. 2 μm<d1<1.7 μm  (136)

2. 0 μm<d1<2.6 μm  (137)

3. 4 μm<d1<4.1 μm  (138)

5. 6 μm<d1<6.5 μm  (139)

6. 9 μm<d1<8.1 μm  (140)

The invention written in item 185 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 181 to 184, the diffractive structure has a function to suppressthe focus position dislocation generated due to the chromatic aberrationof the light converging element, when the first wavelength λ1 changes inthe range of ±10 nm.

The invention written in item 186 is characterized in that: in the lightconverging element for the optical pickup device written in item 185,the paraxial diffraction power PDO (mm⁻¹) to the first wavelength λ1 ofthe diffractive structure, the paraxial diffraction power PD1 (mm⁻¹) tothe wavelength 10 nm longer than the first wavelength λ1 of thediffraction power, the paraxial diffraction power PD2 (mm⁻¹) to thewavelength 10 nm shorter than the first wavelength λ1 of the diffractionpower, satisfy the following expression (141).

PD2<PD0<PD1  (141)

The invention written in item 187 is characterized in that: in the lightconverging element for the optical pickup device written in item 185 or186, the diffractive structure has the wavelength dependency of thespherical aberration like as, when the first wavelength λ1 changestoward the long wavelength side, the spherical aberration changes towardthe under correction direction, and when the first wavelength λ1 changestoward the short wavelength side, the spherical aberration changestoward the over correction direction.

The invention written in item 188 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 181 to 187, the light converging element is a plastic lens, andwhen the diffractive structure has the wavelength dependency of thespherical aberration like as; when the first wavelength λ1 changestoward the long wavelength side, the spherical aberration changes towardthe under correction direction, and when the first wavelength λ1 changestoward the short wavelength side, the spherical aberration changestoward the over correction direction, it has a function to suppress thespherical aberration change generated by the refractive index change ofthe light converging element following the environmental temperaturechange.

The invention written in item 189 is characterized in that: in the lightconverging element for the optical pickup device written in item 188, inthe optical function surfaces of the light converging element, at leastone optical function surface is divided into the central opticalfunction area including the optical axis and the peripheral opticalfunction area surrounding the periphery of the central optical area, andonly in the peripheral optical function area, the diffractive structureis formed.

The invention written in item 190 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 181 to 189, the sectional shape including the optical axis of thediffractive structure is a saw-toothed shape.

The invention written in item 191 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 181 to 190, the superposition type diffractive structure is formedon one optical function surface, and the diffractive structure is formedon another optical function surface of the light converging element.

The invention written in item 192 is characterized in that: it is thelight converging element for the optical pickup device by which thereproducing and/or recording of the information is conducted for thefirst optical information recording medium having the protective layerof thickness t1 by using the light flux of the first wavelength λ1projected from the first light source, the reproducing and/or recordingof the information is conducted for the second optical informationrecording medium having the protective layer of thickness t2 (t2≧t1) byusing the light flux of the second wavelength λ2 (λ2>λ1) projected fromthe second light source, and the reproducing and/or recording of theinformation is conducted for the third optical information recordingmedium having the protective layer of thickness t3 (t3>t2) by using thelight flux of the third wavelength λ3 (λ3>λ2) projected from the thirdlight source; the light converging element is arranged in the positionopposite to the first optical information recording medium to the thirdoptical information recording medium; at least one optical functionsurface in the optical function surfaces of the light converging elementis divided into the plurality of ring-shaped zone-like optical functionareas around the optical axis; in at least one optical function area inthe plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of the ring-shaped zones are continuously arranged around theoptical axis, inside of which a predetermined number of discontinuousstepped sections are formed, is formed; and on at least one opticalfunction surface, in the optical function surfaces of the lightconverging element, the optical path difference grant structure formedof a plurality of ring-shaped zones divided by the stepped section inthe central area including the optical axis and outside the centralarea, is formed.

The invention written in item 193 is characterized in that: in the lightconverging element for the optical pickup device written in item 192,the light converging element is a plastic lens, and when the opticalpath difference grant structure has the temperature dependency of thespherical aberration like as when the environmental temperature rises,the spherical aberration added to the first wavelength λ1 changes towardthe under correction direction, and when the temperature falls, thespherical aberration added to the first wavelength λ1 changes toward theover correction direction, it has a function to suppress the sphericalaberration generated by the refractive index change of the lightconverging element following the environmental temperature change.

The invention written in item 194 is characterized in that: in the lightconverging element for the optical pickup device written in item 193, inthe optical path difference grant structure, the ring-shaped zoneadjoining the outside of the central are is formed by shifting in theoptical axis direction so that the optical path length is shorter to thecentral area, the ring-shaped zone in the maximum effective diameterposition is formed by shifting in the optical axis direction so that theoptical path length is longer to the ring-shaped zone adjoining itsinside, and the ring-shaped zone in the 75% position of the maximumeffective diameter is formed by shifting in the optical axis directionso that the optical path length is shorter to the ring-shaped zoneadjoining its inside and to the ring-shaped zone adjoining its outside.

The invention written in item 195 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 192 to 194, by the first wavelength λ1 (μm), the second wavelengthλ2 (μm), the third wavelength λ3 (μm), the depth d2 (μm) in the opticalaxis direction of the stepped section closest to the optical axis instepped sections of the optical path difference grant structure, therefractive index Nλ1 to the first wavelength λ1 of the light convergingelement, the refractive index Nλ2 to the second wavelength λ2 of thelight converging element, and the refractive index Nλ3 to the thirdwavelength λ3 of the light converging element, Φ1, Φ2, Φ3 respectivelyexpressed by the following expressions (142) to (144) satisfy thefollowing expressions (145) to (148).

Φ1=d2·(Nλ1−1)/λ1  (142)

Φ2=d2·(Nλ2−1)/λ2  (143)

Φ3=d2·(Nλ3−1)/λ3  (144)

INT(Φ1)≦10  (145)

0≦|INT(Φ1)−Φ1|≦0.4  (146)

0≦|INT(Φ2)−Φ2|≦0.4  (147)

0≦|INT(Φ3)−Φ3|≦0.4  (148)

Where, INT (Φi) (i=1, 2, 3) is an integer obtained by half-adjusting Φi.

The invention written in item 196 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 192 to 195, the superposition type diffractive structure is formedon one optical function surface of the light converging element, and theoptical path difference grant structure is formed on another opticalfunction surface of the light converging element.

The invention written in item 197 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 196, the optical function area in which the superpositiontype diffractive structure is formed, is an optical function areaincluding the optical axis.

The invention written in item 198 is characterized in that: in the lightconverging element for the optical pickup device written in item 197, inthe first wavelength λ1 (μm), the second wavelength λ2 (μm), the thirdwavelength λ3 (μm), the superposition type diffractive structure formedin the optical function area including the optical axis, by the number Nof discontinuous stepped sections formed in each ring-shaped zone, thedepth Δ (μm) in the optical axis direction of the discontinuous steppedsection, the refractive index Nλ1 to the first wavelength λ1 of thelight converging element, refractive index Nλ2 to the second wavelengthλ2 of the light converging element, and refractive index Nλ3 to thethird wavelength λ3 of the light converging element, φ1, φ2, φ3respectively expressed by the following expressions (149) to (151)satisfy the following expressions (152) to (154).

φ1=Δ·(Nλ1−1)·(N+1)/λ1  (149)

φ2=Δ·(Nλ2−1)·(N+1)/λ2  (150)

φ3=Δ·(Nλ3−1)·(N+1)/λ3  (151)

0≦|INT(Φ1)−Φ1|≦0.4  (152)

0≦|INT(Φ2)−Φ2|≦0.4  (153)

0≦|INT(Φ3)−Φ3|≦0.4  (154)

Where, INT (Φi) (i=1, 2, 3) is an integer obtained by half-adjusting Φi.

The invention written in item 199 is characterized in that: in the lightconverging element for the optical pickup device written in item 198, Φ1and the number N of the discontinuous steps formed in each ring-shapedzone, satisfy the following expressions (155) and (156).

φ1<24  (155)

3<N<11  (156)

The invention written in item 200 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 197 to 199, the superposition type diffractive structure formed inthe optical function area including the optical axis gives theequivalent first optical action to the light flux of the firstwavelength λ1 and the light flux of the third wavelength λ3, and to thesecond wavelength λ2, gives the second optical action different from thefirst optical action.

The invention written in item 201 is characterized in that: in the lightconverging element for the optical pickup device written in item 200,the first optical action is the 0-degree diffraction by which theoptical path difference is not practically given to the light flux ofthe first wavelength λ1 and the light flux of the third wavelength λ3between adjoining ring-shaped zones, and the second optical action isthe 1st-degree diffraction by which the light flux of the secondwavelength λ2 is diffracted toward the 1st-degree direction.

The invention written in item 202 is characterized in that: in the lightconverging element for the optical pickup device written in item 201,the light converging element is formed of the material in which therefractive index in the first wavelength λ1 s is within the range of1.5-1.6, and Abbe's number on d-line is within the range of 50-60, andthe first wavelength λ1 (μm), second wavelength λ2 (μm), and thirdwavelength λ3 (μm) respectively satisfy the following expressions (157)to (159), and in the superposition type diffractive structure formed inthe optical function area including the optical axis, a combination ofthe number N of discontinuous stepped sections formed in eachring-shaped zone, and the depth D (μm) in the optical axis direction ofthe ring-shaped zone, is respectively any one of the followingexpressions (160)-(163).

0.39<λ1<0.42  (157)

0.63<λ2<0.68  (158)

0.75<λ3<0.85  (159)

When N=3, 4.1≦D≦4.8  (160)

When N=4, 5.4≦D≦6.4  (161)

When N=5, 7.0≦D≦7.9  (162)

When N=6, 8.4≦D≦9.0  (163)

The invention written in item 203 is characterized in that: in the lightconverging element for the optical pickup device written in item 200,the first optical action is the 0-degree diffraction by which theoptical path difference is not practically given to the light flux ofthe first wavelength λ1 and the light flux of the third wavelength λ3between adjoining ring-shaped zones, and the second optical action isthe 2nd diffraction by which the light flux of the second wavelength isdiffracted toward the 2nd-degree direction.

The invention written in item 204 is characterized in that: in the lightconverging element for the optical pickup device written in item 203,the light converging element is formed of the material in which therefractive index in the first wavelength λ1 is within the range of1.5-1.6, and Abbe's number on d-line is within the range of 50-60, andthe first wavelength λ1 (μm), second wavelength λ2 (μm), and thirdwavelength λ3 (μm) respectively satisfy the following expressions (164)to (166), and in the superposition type diffractive structure formed inthe optical function area including the optical axis, the number N ofdiscontinuous stepped sections formed in each ring-shaped zone, and thedepth D (μm) in the optical axis direction of the ring-shaped zone, arerespectively any one of the following expressions (167)-(170).

0.39<λ1<0.42  (164)

0.63<λ2<0.68  (165)

0.75<λ3<0.85  (166)

When N=8, 11.3≦D≦12.7  (167)

When N=9, 12.8≦D≦14.1  (168)

When N=10, 14.2≦D≦15.6  (169)

When N=11, 15.7≦D≦17.2  (170)

The invention written in item 205 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 197 to 204, the superposition type diffractive structure is formedin all of the plurality of optical function areas.

The invention written in item 206 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 204, in at least one optical function area in the pluralityof optical function areas, the superposition type diffractive structureis not formed.

The invention written in item 207 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 206, the superposition type diffractive structure is formedon the plurality of optical function surfaces of the aberrationcorrecting element.

The invention written in item 208 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 207, the thickness t1 of the protective layer of the firstoptical information recording medium and the thickness t2 of theprotective layer of the second optical information recording mediumsatisfy the following expression (171).

0.8≦t1/t2<1.2  (171)

The invention written in item 209 is characterized in that: in the lightconverging element for the optical pickup device written in item 208,the plurality of optical function areas are 2 optical function areas,and the light flux of the first wavelength λ1 to the light flux of thethird wavelength λ3, which are incident on the optical function areasincluding the optical axis, respectively form good wave-fronts on theinformation recording surfaces of the first optical informationrecording medium to the third optical information recording medium, andin the two optical function areas, the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2, which areincident on the optical function areas not including the optical axis,respectively form good wave-fronts on the information recording surfacesof the first optical information recording medium and the second opticalinformation recording medium.

The invention written in item 210 is characterized in that: in the lightconverging element for the optical pickup device written in item 209,the superposition type diffractive structure is formed in the opticalfunction area not including the optical axis in 2 optical functionareas, and the diffraction efficiency η3 of the diffracted light rayhaving the maximum diffraction efficiency in the diffracted light raygenerated when the light flux of the third wavelength λ3 enters into thesuperposition type diffractive structure, is not larger then 40%.

The invention written in item 211 is characterized in that: in the lightconverging element for the optical pickup device written in item 209 or210, in 2 optical function areas, the superposition type diffractivestructure is formed in the optical function area not including theoptical axis, and when the superposition type diffractive structuregives the equivalent optical action to the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2, and to thelight flux of the third wavelength λ3, gives the optical actiondifferent from the above-described optical action, the light flux of thethird wavelength λ3 transmitted the superposition type diffractivestructure is made a flare component which does not contribute to thespot formation onto the information recording surface of the thirdoptical information recording medium.

The invention written in item 212 is characterized in that: in the lightconverging element for the optical pickup device written in item 208,the plurality of optical function areas are 3 optical function areas,and in 3 optical function areas, the light flux of the wavelength λ1 tothe light flux of the third wavelength λ3 which are incident on theoptical function area including the optical axis, respectively form goodwave-front on the information recording surfaces of the first opticalinformation recording medium to third optical information recordingmedium, and in 3 optical function areas, the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2 which areincident on optical function areas adjoining the outside of the opticalfunction area including the optical axis, respectively form the goodwave-front on the information recording surfaces of the first opticalinformation recording medium and second optical information recordingmedium, and the light flux of the first wavelength λ1 incident on themost outside optical function area in 3 optical function areas, formsthe good wave-front on the information recording surface of the firstoptical information recording medium.

The invention written in item 213 is characterized in that: in the lightconverging element for the optical pickup device written in item 212, in3 optical function areas, in the optical function area adjoining theoutside of the optical function area including the optical axis, thesuperposition type diffractive structure is formed, and the diffractionefficiency η3 of the diffracted light ray having the maximum diffractionefficiency in the diffracted light ray generated when the light flux ofthe third wavelength λ3 enters into the superposition type diffractivestructure, is not larger than 40%.

The invention written in item 214 is characterized in that: in the lightconverging element for the optical pickup device written in item 212 or213, in 3 optical function areas, in the optical function area adjoiningthe outside of the optical function area including the optical axis, thesuperposition type diffractive structure is formed, and when thesuperposition type diffractive structure gives the equivalent opticalaction to the light flux of the first wavelength λ1 and the light fluxof the second wavelength λ2, and to the light flux of the thirdwavelength λ3, gives the optical action different from theabove-described optical action, the light flux of the third wavelengthλ3 which transmitted the superposition type diffractive structure, ismade a flare component which does not contribute to the spot formationonto the information recording surface of the third optical informationrecording medium.

The invention written in item 215 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 212 to 214, in 3 optical function areas, in the most outsideoptical function area, the superposition type diffractive structure isformed, and the diffraction efficiency η2 of the diffracted light rayhaving the maximum diffraction efficiency in the diffracted light raygenerated when the light flux of the second wavelength λ2 enters intothe superposition type diffractive structure, is not larger than 40%,and the diffraction efficiency λ3 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the third wavelength λ3 enters into thesuperposition type diffractive structure, is not larger than 40%.

The invention written in item 216 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 212 to 215, in 3 optical function areas, in the most outsideoptical function area, the superposition type diffractive structure isformed, and when the superposition type diffractive structure gives theoptical action different from the optical action given to the light fluxof the first wavelength λ1 to the light flux of the first wavelength λ2and the light flux of the second wavelength λ3, the light fluxes of thesecond wavelength λ2 and the third wavelength λ3 which transmitted thesuperposition type diffractive structure, are respectively made flarecomponents which do not contribute to the spot formation onto theinformation recording surfaces of the second optical informationrecording medium and the third optical information recording medium.

The invention written in item 217 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 207, the thickness t1 of the protective layer of the firstoptical information recording medium and the thickness t2 of theprotective layer of the second optical information recording mediumsatisfy the following expression (172).

t1/t2≦0.4  (172)

The invention written in item 218 is characterized in that: in the lightconverging element for the optical pickup device written in item 217,the plurality of optical function areas are 3 optical function areas,and the light flux of the first wavelength λ1 to the light flux of thethird wavelength λ3, which are incident on the optical function areasincluding the optical axis in 3 optical function areas, respectivelyform good wave-fronts on the information recording surfaces of the firstoptical information recording medium to the third optical informationrecording medium, and in 3 optical function areas, the light flux of thefirst wavelength λ1 and the light flux of the second wavelength λ2,which are incident on the optical function areas adjoining the outsideof the optical function area including the optical axis, respectivelyform good wave-fronts on the information recording surfaces of the firstoptical information recording medium and the second optical informationrecording medium, and in 3 optical function areas, the light flux of thefirst wavelength λ1 which enters in the most outside optical functionarea, forms a good wave-front on the information recording surface ofthe first optical information recording medium.

The invention written in item 219 is characterized in that: in the lightconverging element for the optical pickup device written in item 218,the superposition type diffractive structure is formed in the opticalfunction area adjoining the outside of the optical function areaincluding the optical axis in 3 optical function areas, and thediffraction efficiency η3 of the diffracted light ray having the maximumdiffraction efficiency in the diffracted light ray generated when thelight flux of the third wavelength λ3 enters into the superposition typediffractive structure, is not larger then 40%.

The invention written in item 220 is characterized in that: in the lightconverging element for the optical pickup device written in item 218 or219, in 3 optical function areas, in the optical function area adjoiningthe outside of the optical function area including the optical axis, thesuperposition type diffractive structure is formed, and when thesuperposition type diffractive structure gives the equivalent opticalaction to the light flux of the first wavelength λ1 and the light fluxof the second wavelength λ2, and to the light flux of the thirdwavelength λ3, gives the optical action different from theabove-described optical action, the light flux of the third wavelengthλ3 which transmitted the superposition type diffractive structure, ismade a flare component which does not contribute to the spot formationonto the information recording surface of the third optical informationrecording medium.

The invention written in item 221 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 218 to 220, the superposition type diffractive structure is formedin the most outside optical function area, in 3 optical function areas,and the diffraction efficiency η2 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the second wavelength λ2 enters into thesuperposition type diffractive structure, is not larger then 40%, andthe diffraction efficiency λ3 of the diffracted light ray having themaximum diffraction efficiency in the diffracted light ray generatedwhen the light flux of the third wavelength λ3 enters into thesuperposition type diffractive structure, is not larger then 40%.

The invention written in item 222 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 218 to 221, in 3 optical function areas, in the most outsideoptical function area, the superposition type diffractive structure isformed, and when the superposition type diffractive structure gives theoptical action different from the optical action given to the light fluxof the first wavelength λ1, to the light flux of the second wavelengthλ2 and the light flux of the third wavelength λ3, the light fluxes ofthe second wavelength λ2 and third wavelength λ3 which transmitted thesuperposition type diffractive structure, are respectively made flarecomponents which do not contribute to the spot formation ontoinformation recording surfaces of the second optical informationrecording medium and the third optical information recording medium.

The invention written in item 223 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 222, the light converging element is a plastic lens.

The invention written in item 224 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 222, the light converging element is a glass lens whoseglass transition point Tg is not higher than 400° C.

The invention written in item 225 is characterized in that: in the lightconverging element for the optical pickup device written in any one ofitems 163 to 223, the light converging element is molded by using amaterial in which particles whose diameter is not larger than 30 nm, aredispersed in the plastic material.

The invention written in item 226 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; the optical pickup device has theobjective optical system for the purpose by which the light fluxes ofthe first wavelength λ1 to the third wavelength λ3 are respectivelylight-converged on the information recording surfaces of the firstoptical information recording medium to the third optical informationrecording medium; and as the objective optical system, the lightconverging element written in any one of items 163 to 225 is used.

The invention written in item 227 is characterized in that: the opticalpickup device written in item 226 is mounted, and at least one of therecording of the information for the first optical information recordingmedium to the third optical information recording medium, and thereproducing of the information for the first optical informationrecording medium to the third optical information recording medium, canbe conducted.

The invention written in item 228 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; the optical pickup device has theobjective optical system for the purpose by which the light fluxes ofthe first wavelength λ1 to the third wavelength λ3 are respectivelylight-converged on the information recording surfaces of the firstoptical information recording medium to the third optical informationrecording medium, stop, and drive device to integrally drive theobjective optical system and the stop in the direction perpendicular tothe optical axis; in the objective optical system, at least one opticalfunction surface in the optical function surfaces is divided into theplurality of ring-shaped zone-like optical function areas around theoptical axis; in the optical function area including the optical axis inthe plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of the ring-shaped zones are continuously arranged around theoptical axis, inside of which a predetermined number of discontinuousstepped sections are formed, is formed; and has a structure in which atleast one light flux of light fluxes of the first wavelength λ1 to thethird wavelength λ3 enters into the objective optical system in thenon-parallel situation; in the first light source to the third lightsource, in the optical path between at least one light source of thelight sources which project light fluxes incident on the objectiveoptical system in non-parallel situation, and the objective opticalsystem, the coma correcting element having a function to reduce the comagenerated when the objective optical system is driven by the drivedevice in the direction perpendicular to the optical axis, is arranged.

The invention written in item 229 is characterized in that: in theoptical pickup device written in item 228, when the objective opticalsystem is not driven in the direction perpendicular to the optical axisby the drive device, the coma correcting element has the sphericalaberration which is corrected so that it is not larger than diffractionlimit, in the effective diameter in which the light flux incident on theobjective optical system in non-parallel situation passes, and outsidethe effective diameter, has the spherical aberration in the overcorrection direction.

The invention written in item 230 is characterized in that: in theoptical pickup device written in item 229, the light flux incident onthe objective optical system in non-parallel situation, is a diverginglight flux.

The invention written in item 231 is characterized in that: in theoptical pickup device written in item 229 or 230, the light fluxincident on the objective optical system in non-parallel situation, isthe light flux of the third wavelength λ3.

The invention written in item 232 is characterized in that: in theoptical pickup device written in any one of items 229 to 231, the lightflux incident on the objective optical system in non-parallel situation,is the light flux of the second wavelength λ2.

The invention written in item 233 is characterized in that: in theoptical pickup device written in any one of items 229 to 232, the lightflux incident on the objective optical system in non-parallel situation,is the light flux of the second wavelength λ2 and the light flux of thethird wavelength λ3.

The invention written in item 234 is characterized in that: in theoptical pickup device written in item 233, the coma correcting elementis arranged in a common optical path of the light flux of the secondwavelength λ2 and the light flux of the third wavelength λ3; when theobjective optical system is not driven in the direction perpendicular tothe optical axis by the drive device, in the effective diameter throughwhich the second wavelength λ2 which enters into the objective opticalsystem in non-parallel situation, passes, the spherical aberration ofthe wavelength λ2 is corrected so that it is not larger than thediffraction limit, and outside the effective diameter, the sphericalaberration of the wavelength λ2 is corrected in the over correctiondirection, and when the objective optical system is not driven in thedirection perpendicular to the optical axis by the drive device, in theeffective diameter through which the second wavelength λ3 which entersinto the objective optical system in non-parallel situation, passes, thespherical aberration of the wavelength λ3 is corrected so that it is notlarger than the diffraction limit, and outside the effective diameter,the spherical aberration of the wavelength λ3 is corrected in the overcorrection direction.

The invention written in item 235 is characterized in that: in theoptical pickup device written in item 233 or 234, on at least oneoptical function surface of the coma correcting element, the diffractivestructure formed of a plurality of ring-shaped zones divided by thestepped section around the optical axis, is formed.

The invention written in item 236 is characterized in that: in theoptical pickup device written in any one of items 233 to 235, the secondlight source and the third light source are packaged light sourcemodule.

The invention written in item 237 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; the optical pickup device has theobjective optical system for the purpose by which the light fluxes ofthe first wavelength λ1 to the third wavelength λ3 are respectivelylight-converged on the information recording surfaces of the firstoptical information recording medium to the third optical informationrecording medium; in the objective optical system, at least one opticalfunction surface in the optical function surfaces is divided into aplurality of ring-shaped zone-like optical function areas around theoptical axis; in the optical function area including the optical axis inthe plurality of ring-shaped zone-like optical function areas, thesuperposition type diffractive structure which is a structure in which aplurality of the ring-shaped zones are continuously arranged around theoptical axis, inside of which a predetermined number of discontinuousstepped sections are formed, is formed; and has a structure in which atleast two light fluxes of light fluxes of the first wavelength λ1 to thethird wavelength λ3 are incident on the objective optical system in themagnification different from each other; in the first light source tothe third light source, the light sources from which at least two lightfluxes incident on the objective optical system in the magnificationdifferent from each other, are projected, are a packaged light sourcemodule; and a diverging angle conversion element for the purpose bywhich the diverging angle of at least one light flux in light fluxesprojected from the light source module is converted, and guided to theobjective optical system in which the superposition type diffractivestructure which is a structure in which a plurality of the ring-shapedzones are continuously arranged around the optical axis, inside of whicha predetermined number of discontinuous stepped sections are formed, isformed, on at least one optical function surface, is arranged in theoptical path between the light source module and the objective opticalsystem.

The invention written in item 238 is characterized in that: in theoptical pickup device written in item 237, the superposition typediffractive structure formed in the diverging angle conversion element,gives the first optical action to a one light flux in light fluxesprojected from the light source module, and to the light fluxes of theother wavelengths, gives the second optical action different from thefirst optical action.

The invention written in item 239 is characterized in that: in theoptical pickup device written in item 238, the light fluxes projectedfrom the light source module, are 2 light fluxes, and 2 light fluxes arethe light flux of the first wavelength λ1 and the light flux of thesecond wavelength λ2.

The invention written in item 240 is characterized in that: in theoptical pickup device written in item 238, the light fluxes projectedfrom the light source module, are 2 light fluxes, and 2 light fluxes arethe light flux of the second wavelength λ2 and the light flux of thethird wavelength λ3.

The invention written in item 241 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 115, on at least one optical function surface in opticalfunction surfaces of the optical element, a wavelength selection filteris formed, and the optical function surface on which the wavelengthselection filter is formed, is divided into an optical function areaincluding the optical axis, and the peripheral optical function areasurrounding its periphery, and the wavelength selection filter has thewavelength selectivity of the transmission factor by which the lightflux of the first wavelength λ1 to the light flux of the thirdwavelength λ3, are transmitted in the optical function area includingthe optical axis, and in the peripheral optical function areas, thelight flux of the third wavelength λ3 is cut off or reflected, and thelight flux of the first wavelength λ1 and the light flux of the secondwavelength λ2 are transmitted.

The invention written in item 242 is characterized in that: in theoptical element for the optical pickup device written in any one ofitems 45 to 115, on at least one optical function surface in opticalfunction surfaces of the optical element, a wavelength selection filteris formed, and the optical function surface on which the wavelengthselection filter is formed, is divided into an optical function areaincluding the optical axis, the first peripheral optical function areasurrounding its periphery, and the second peripheral optical functionarea further surrounding its periphery; and the wavelength selectionfilter has the wavelength selectivity of the transmission factor bywhich the light flux of the first wavelength λ1 to the light flux of thewavelength λ3 are transmitted, in the optical function area includingthe optical axis, and in the first peripheral optical function area, thelight flux of the third wavelength λ3 is cut off or reflected, and thelight flux of the first wavelength λ1 and the light flux of the secondwavelength λ2 are transmitted, and in the second peripheral opticalfunction area, the light flux of the second wavelength λ2 and the lightflux of the third wavelength λ3 are cut off or reflected, and the lightflux of the first wavelength λ1 is transmitted.

The invention written in item 243 is characterized in that: in theoptical element for the optical pickup device written in item 241 or242, the wavelength selection filter is formed on at least one opticalfunction surface of the aberration correcting element.

The invention written in item 244 is characterized in that: in theoptical element for the optical pickup device written in item 241 or242, the wavelength selection filter is formed on at least one opticalfunction surface of the light converging element.

The invention written in item 245 is characterized in that: in theoptical pickup device written in item 116, the optical pickup device hasan aperture limit element arranged on the light flux incident surfaceside of the objective optical system; on at least one optical functionsurface of the aperture limit element, the wavelength selection filteris formed; the optical function surface on which the wavelengthselection filter is formed, is divided into the optical function areaincluding the optical axis, and the peripheral optical function areasurrounding its periphery; the wavelength selection filter has thewavelength selectivity of the transmission factor by which the lightflux of the wavelength λ1 to the light flux of the wavelength λ3 aretransmitted, in the optical function area including the optical axis,and in the peripheral optical function area, the light flux of the thirdwavelength λ3 is cut off or reflected, and the light flux of thewavelength λ1 and the light flux of the second wavelength λ2 aretransmitted.

The invention written in item 246 is characterized in that: in theoptical pickup device written in item 116, the optical pickup device hasan aperture limit element arranged on the light flux incident surfaceside of the objective optical system; on at least one optical functionsurface of the aperture limit element, the wavelength selection filteris formed; the optical pickup device has an aperture limit elementarranged on the light flux incident surface side of the objectiveoptical system; on at least one optical function surface of the aperturelimit element, the wavelength selection filter is formed; the opticalfunction surface on which the wavelength selection filter is formed, isdivided into the optical function area including the optical axis, thefirst peripheral optical function area surrounding its periphery, andthe second peripheral optical function area further surrounding itsperiphery; the wavelength selection filter has the wavelengthselectivity of the transmission factor by which, in the optical functionarea including the optical axis, the light flux of the first wavelengthλ1 to the light flux of the third wavelength λ3 are transmitted, in thefirst peripheral optical function area, the light flux of the thirdwavelength λ3 is cut off or reflected, and the light flux of the firstwavelength λ1 and the light flux of the second wavelength λ2 aretransmitted, and in the second peripheral optical function area, thelight flux of the second wavelength λ2 and the light flux of the thirdwavelength λ3 are cut off or reflected, and the light flux of the firstwavelength λ1 is transmitted.

The invention written in item 247 is characterized in that: in theoptical pickup device written in item 245 or 246, the optical pickupdevice has a drive device to drive the objective optical system at leastin the direction perpendicular to the optical axis, and the aperturelimit element is driven integrally with the objective optical system inthe direction perpendicular to the optical axis by the drive device.

The invention written in item 248 is characterized in that: it is anoptical pickup device by which the reproducing and/or recording of theinformation is conducted for the first optical information recordingmedium having the protective layer of thickness t1 by using the lightflux of the first wavelength λ1 projected from the first light source,the reproducing and/or recording of the information is conducted for thesecond optical information recording medium having the protective layerof thickness t2 (t2≧t1) by using the light flux of the second wavelengthλ2 (λ2>λ1) projected from the second light source, and the reproducingand/or recording of the information is conducted for the third opticalinformation recording medium having the protective layer of thickness t3(t3>t2) by using the light flux of the third wavelength λ3 (λ3>λ2)projected from the third light source; the optical pickup device is astructure in which a plurality of ring-shaped zones inside of which apredetermined number of discontinuous stepped sections are formed, arecontinuously arranged around the optical axis, and has a diffractionlens having at least one optical surface on which the superposition typediffractive structure which practically dose not give the phasedifference to the first light flux and the third light flux, and to onlythe second light flux, gives the phase difference, is formed, and alight converging element to light-converge the light fluxes of the firstwavelength λ1 to the third wavelength λ3 respectively onto theinformation recording surfaces of the first optical informationrecording medium to the third optical information recording medium; andwhen the magnification to the light flux of the first wavelength λ1 ofthe optical system structured by the diffraction lens and the lightconverging element, is made m1, the magnification to the light flux ofthe second wavelength λ2 of the optical system structured by thediffraction lens and the light converging element, is made m2, and themagnification to the light flux of the third wavelength λ3 of theoptical system structured by the diffraction lens and the lightconverging element, is made m3, the following expression (173) issatisfied.

m1≧m2>m3  (173)

The invention written in item 249 is characterized in that: in theoptical pickup device written in item 248, the following expression(174) is satisfied.

m1=m2  (174)

The invention written in item 250 is characterized in that: in theoptical pickup device written in item 248, the following expressions(175) and (176) are satisfied.

m1=m2=0  (175)

−0.25<m3<−0.10  (176)

According to the invention of item 248, when the magnification m3 of theoptical system structured by the diffraction lens and the lightconverging element, to the third flux is set so as to satisfy theexpression (173), the spherical aberration generated due to thedifference of the thickness of the protective layer between the highdensity optical disk and CD, can be corrected.

Hereupon, because the second light flux used for therecording/reproducing of the information for DVD is subjected to thediffraction action when the phase difference is added by thesuperposition type diffractive structure, by such a diffraction action,the spherical aberration generated due to the difference of thethickness of the protective layer between the high density optical diskand DVD can be corrected.

In order to make the characteristic of the optical pickup device good,and further, to make the design and production of the optical pickupdevice easy, as in the invention of item 249, it is preferable thatmagnifications m1 and m2 of the optical system structured by thediffraction lens and the light converging element to the first lightflux and the second light flux are made the same magnification as in theexpression (174).

More preferably, as in the invention of item 250, magnifications m1 andm2 of the optical system structured by the diffraction lens and thelight converging element to the first light flux and the second lightflux are made 0 as in the expression (175), and in this case, it ispreferable that the magnification m3 to the third light flux is set soas to satisfy the expression (176).

The invention described in Item 251 is an optical pickup deviceconducting reproducing and/or recording of information for the firstoptical information recording medium having a t1-thick protective layerby using a light flux with first wavelength λ1 emitted from the firstlight source, reproducing and/or recording of information for the secondoptical information recording medium having a t2-thick protective layer(t2≧t1) by using a light flux with second wavelength λ2 (λ2>λ1) emittedfrom the second light source, and reproducing and/or recording ofinformation for the third optical information recording medium having at3-thick protective layer (t3>t2) by using a light flux with thirdwavelength λ3 (λ3>λ2) emitted from the third light source, wherein theoptical pickup device has therein a light-converging element forconverging each of light fluxes having respectively the first wavelengthλ1-third wavelength λ3 on an information recording surface of each ofthe first-third information recording media, an aberration correctingmeans having a phase structure and asphericalal aberration correctingmeans, while, the aberration correcting means has a function to correctspherical aberration caused on the light-converging element by adifference between the first wavelength λ1 and the second wavelength λ2and/or spherical aberration caused by a difference between t1 and t2,and the spherical aberration correcting means has a function to correctspherical aberration caused by a difference between t1 and t3.

The invention described in Item 252 is the optical pickup devicedescribed in Item 251, wherein the phase structure is either one of asuperposed diffractive structure, a diffractive structure and an opticalpath difference providing structure.

The invention described in Item 253 is the optical pickup devicedescribed in Item 252, wherein an optical path difference added to thefirst light flux by the phase structure is an integer multiple of thefirst wavelength λ1.

The invention described in Item 254 is the optical pickup devicedescribed in Item 253, wherein an optical path difference added to thefirst light flux by the phase structure is even multiples of the firstwavelength λ1.

The invention described in Item 255 is the optical pickup devicedescribed in Item 254, wherein the optical pickup device further has asecond aberration correcting element that has a second phase structurewhich is either one of the diffractive structure and the optical pathdifference providing structure, and an optical path difference added tothe first light flux by the second phase structure is odd multiples ofthe first wavelength λ1.

The invention described in Item 256 is the optical pickup devicedescribed in either one of Item 251-Item 255, wherein magnification m1of an optical system composed of the light-converging element and theaberration correcting element for the first wavelength λ1 agreessubstantially with magnification m2 for the second wavelength λ2.

The invention described in Item 257 is the optical pickup devicedescribed in either one of Item 251-Item 256, wherein thelight-converging element is optimized in terms of spherical aberrationcorrection for the first wavelength λ1 and for the t1-thick protectivelayer.

The invention described in Item 258 is the optical pickup devicedescribed in either one of Item 251-Item 257, wherein thelight-converging element and the aberration correcting element are heldso that their relative positional relationship may not be changed.

The invention described in Item 259 is the optical pickup devicedescribed in either one of Item 251-Item 258, wherein the sphericalaberration correcting means is a liquid crystal phase control elementcomposed of a liquid crystal layer that causes a phase change on a lightflux that is transmitted by voltage impression and of electrode layersfacing each other for impressing voltage, and the liquid crystal phasecontrol element corrects spherical aberration caused by a differencebetween the thickness t1 and the thickness t3 by controlling the phaseof the third light flux.

The invention described in Item 260 is the optical pickup devicedescribed in Item 259, wherein the liquid crystal phase control elementconducts only phase control of the third light flux selectively.

The invention described in Item 261 is the optical pickup devicedescribed in either one of Item 251-Item 258, wherein the sphericalaberration correcting means is a movable lens unit composed of anactuator and a movable lens group that can be moved by the actuator atleast in the optical axis direction, and the movable lens unit correctsspherical aberration caused by a difference between the thickness t1 andthe thickness t3, by changing the magnification of the light-convergingelement.

The invention described in Item 262 is the optical pickup devicedescribed in Item 261, wherein magnification m3 of the light-convergingelement for the third wavelength λ3 satisfies the following expression(177).

−0.15<m3<−0.02  (177)

The invention described in Item 263 is the optical pickup devicedescribed in either one of Item 251-Item 261, wherein at least two ofthe first light source—the third light source are integrated solidly.

The invention described in Item 264 is the optical pickup devicedescribed in Item 263, wherein all of the first light source-the thirdlight source are integrated solidly.

In the invention described in Item 251, it is possible to make the firstoptical information recording medium (for example, a high densityoptical disc) and the second optical information recording medium (forexample, DVD) to be compatible, by the functions of the phase structure,and it is possible to make the first optical information recordingmedium (for example, a high density optical disc) and the third opticalinformation recording medium (for example, CD) to be compatible, by thefunctions of the spherical aberration correcting means. In this case,the phase structure has a function to correct spherical aberrationcaused by a difference between the first wavelength λ1 and the secondwavelength λ2 and/or spherical aberration caused by a difference betweent1 and t2. The former corresponds to the occasion where t1 and t2 arethe same each other (for example, HD DVD with t1=0.6 mm and DVD witht2=0.6 mm), while, the latter corresponds to the occasion where t1 andt2 are different each other (for example, a blue ray disc with t1=0.1 mmand DVD with t2=0.6 mm).

The phase structure may be either one of the superposed diffractivestructure shown schematically in FIG. 26, the diffractive structureshown schematically in FIG. 27 and the optical path difference providingstructure shown schematically in FIG. 28, as in the invention describedin Item 252.

It is further preferable to design the phase structure so that anoptical path difference added to the first light flux when passingthrough the phase structure may be an integer multiple of the firstwavelength λ1, as shown in the invention in Item 253. Due to this, adecline of transmittance of the phase structure for the first light fluxcan be prevented.

It is possible to prevent also a decline of transmittance of a phasestructure for the second light flux and the third light flux if thephase structure is designed in advance so that an optical pathdifference added to the first light flux when passing through the phasestructure may be even multiples of the first wavelength λ1, as shown inthe invention in Item 254.

However, if the phase structure is designed so that an optical pathdifference to be added to the first light flux may be even multiples ofthe first wavelength λ1, actions to be added to the first light flux andto the third light flux both passing through the phase structure becomethe same each other. Therefore, it is impossible for the phase structureto reduce spherical aberration caused by a difference between t1 and t3,which increases a burden for the spherical aberration correcting means.

It is therefore preferable to arrange the second aberration correctingelement having the second phase structure which is either one of adiffractive structure and an optical path difference providingstructure, and to design the second phase structure so that an opticalpath difference added to the first light flux may be odd multiples ofthe first wavelength λ1 when passing through the second phase structure,as shown in the invention described in Item 255. In this case, when thethird light flux passes through the second phase structure, an opticalpath difference that is a half integer multiple of λ3 is added. Due tothis, it is possible to reduce spherical aberration caused by adifference between t1 and t3 and thereby to lower a burden for thespherical aberration correcting means, because it is possible to addactions which are different from those for the first light flux to thethird light flux that is transmitted through the second phase structure,although the transmittance of the second phase structure for the thirdlight flux is lowered. Since the spherical aberration caused by adifference between t1 and t3 can be lowered by the phase structure asstated above, an absolute value of magnification m3 of thelight-converging element for the third light flux λ3 does not become toogreat when using a movable lens unit having a lens group movable in theoptical axis direction by an actuator described in the invention in Item260 that will be stated later, resulting in an acquisition of excellenttracking characteristics of the light-converging element.

When the phase structure is a superposed diffractive structure, it ispreferable to establish depth Δ of a step in each ring-shaped zone inthe optical axis direction so that Δ=2m·λ1/(Nλ1−1) may be satisfiedsubstantially, by making the number of division in each ring-shaped zoneto be either one of 4, 5 and 6 (namely, by making the number of steps ineach ring-shaped zone to be either one of 3, 4 and 5), and it is mostpreferable to make m=1 to hold under the condition that the number ofdivision in each ring-shaped zone is 5. Due to this, it is possible toattain compatibility between the first optical information recordingmedium and the second optical information recording medium and tocontrol a decline of transmittance of the phase structure for the secondlight flux to be small, because the second light flux alone is given aphase difference and is diffracted when passing through the superposeddiffractive structure. Incidentally, the symbol m stated aboverepresents a positive integer of 5 or less and Nλ1 represents adiffractive index of the aberration correcting element for the firstwavelength λ1.

When the phase structure is a diffractive structure, it is preferable toestablish a depth of a step of each ring-shaped zone so that thefollowing relationship may be satisfied by diffraction order n1 ofdiffracted light ray generated when the first light flux enters,diffraction order n2 of diffracted light ray generated when the secondlight flux enters and diffraction order n3 of diffracted light raygenerated when the third light flux enters.

n1≧n2≧n3

Incidentally, the diffraction order mentioned here means a diffractionorder of a diffracted light ray having the maximum diffractionefficiency among various diffracted light ray having respectivelyvarious diffraction orders generated by the diffractive structure. Amongcombinations of these diffraction orders, the preferable ones include(n1, n2, n3) (1, 1, 1), (2, 1, 1), (3, 2, 1), (3, 2, 2), (8, 5, 4). Tosecure high diffraction efficiencies for all of the first light flux—thethird light flux, combinations of (n1, n2, n3)=(2, 1, 1) and (8, 5, 4)are especially preferable.

When the phase structure is an optical path difference providingstructure, it is preferable to make an optical path difference betweenring-shaped zones adjoining each other (a wavelength of each light fluxis expressed as a unit) to be either one of (Φ1, Φ2, Φ3)=(1λ1, 1λ2,1λ3), (2λ1, 1λ2, 1λ3), (3λ1, 2λ2, 1λ3), (3λ1, 2λ2, 2λ3), (8λ1, 5λ2,4λ3), when Φ1 is for the first light flux, Φ2 is for the second lightflux and Φ3 is for the third light flux. To secure high diffractionefficiencies for all of the first light flux-the third light flux,combinations of (Φ1, Φ2, Φ3=(2λ1, 1λ2, 1λ3), (8λ1, 5λ2, 4λ3) areespecially preferable.

The invention described in Item 256 makes it possible to make opticalparts for the first light flux and optical parts for the second lightflux to be common each other and thereby to simplify the structure ofthe optical pickup device, because a conjugated length of the opticalsystem composed of a light-converging element and an aberrationcorrecting element can be made the same for the first light flux and thesecond light flux.

In general, with respect to an optical element, the shorter the workingwavelength is, the more strict the accuracy required for the opticalelement is. As shown in the invention described in Item 257, it becomeseasy to attain characteristics of the light-converging element that isrequired to have especially high accuracy, by optimizing thelight-converging element for the first wavelength λ1 and for thicknesst1 of a protective layer.

When the first optical information recording medium and the secondoptical information recording medium are used on a compatible basis byactions of the phase structure, coma-aberration is easily generated byeccentricity between a light-converging element and an aberrationcorrecting element in the direction perpendicular to the optical axisdirection. As shown in the invention described in Item 258, generationof the aforementioned coma-aberration can be controlled by conductingtracking drive by integrating the light converging element and theaberration correcting element solidly, and excellent trackingcharacteristics can be obtained.

As a method for integrating the light-converging element and theaberration correcting element solidly, flange portions of respectiveelements may be cemented, or both elements may be integrated through aseparate cementing member, or each element may be incorporated in abobbin to be integrated solidly.

As asphericalal aberration correcting means for using the first opticalinformation recording medium and the third optical information recordingmedium on a compatible basis, it is possible to use a liquid crystalphase control means which controls a phase of the transmitted thirdlight flux by impressing voltage on a liquid crystal layer, such as thatdescribed in the invention in Item 259. The liquid crystal phase controlmeans of this kind is advantageous for downsizing of the optical pickupdevice, because no mechanically movable portion is needed.

Since the spherical aberration is increased in proportion to the fourthpower of the effective diameter (namely, numerical aperture NA of thelight-converging element), if the liquid crystal phase control elementis used in common for both the first light flux with a large effectivediameter and the third light flux with a small effective diameter,correction of spherical aberration for the third light flux becomesinsufficient, which is a problem that is getting more and more obvious.“Used in common” mentioned here means actions to conduct phase controlfor each light flux having its own wavelength. For example, when addingspherical aberration of ±0.2λRMS (λ=λ1) to the first light flux underthe condition that the third wavelength λ3 is 785 nm, numerical apertureNA of CD is 0.45, the first wavelength λ1 is 405 nm and numericalaperture NA of a high density optical disc is 0.85, the sphericalaberration which can be added to the third light flux is about ±0.01λRMS(λ=λ3) (=±0.2×{(0.45⁴/785)/(0.85⁴/405)}). Since the spherical aberrationcapable of being corrected by a liquid crystal phase control element isabout +0.2 ARMS, when a liquid crystal phase element is used commonlyfor the first and third light fluxes, an amount of adding sphericalaberration for the third light flux is insufficient, and compatibilitybetween the first optical information recording medium and the thirdoptical information recording medium is lost. It is therefore preferableto arrange the structure wherein only phase control for the third lightflux is conducted selectively as shown in the invention in Item 260, andto add sufficient spherical aberration to the third light flux.

As asphericalal aberration correcting means that conducts compatibilitybetween the first optical information recording medium and the thirdoptical information recording medium, a movable lens unit having a lensgroup that can be moved in the optical axis direction by an actuatordescribed in the invention in Item 261 may also be used. Since themovable lens unit corrects spherical aberration caused by a differencebetween t1 and t3 by changing magnification of the light-convergingelement, there is no occurrence of coma caused by optical axis deviationfrom the light-converging element, and it is not necessary to drivetracking solidly with the light-converging element, which isadvantageous.

A specific embodiment of this movable lens unit may include a couplinglens that converts an angle of divergence of a divergent light fluxemitted from the third light source and guides it to a light-convergingelement, a collimator lens that converts a divergent light flux emittedfrom the third light source into a parallel light flux and guides it toa light-converging element, or a beam expander arranged in the opticalpath located between the coupling lens that converts an angle ofdivergence of a divergent light flux emitted from the third light sourceand guides it to a light-converging element and the light-convergingelement.

In particular, by arranging the aforementioned movable lens in thecommon optical path through which the first-third light fluxes pass, itis possible to correct wavelength dispersion caused by manufacturingerrors for the first light source, refractive index changes andrefractive index distribution of the light-converging element caused bytemperature changes, focus jump between layers in recording/reproducingfor multi-layer optical information recording media such as of 2-layerand 4-layer types and spherical aberration caused by thicknessdispersion resulting from manufacturing errors for protective layers ofthe first optical information recording medium and from thicknessdistribution, thus, recording/reproducing characteristics for the firstoptical information recording medium can be improved.

As an actuator that moves the movable lens group stated above, astepping motor, a solenoid, a voice coil actuator and an actuatoremploying a piezoelectric element can be used. Since a technology tomove an optical element by a stepping motor or by a voice coil actuatorin the optical axis direction is publicly known, detailed explanationtherefor will be omitted here. Further, as an actuator employing apiezoelectric element, it is possible to use a small-sized linearactuator employing a piezoelectric element such as one described in thefollowing document.

OPTICS DESIGN, No. 26, 16-21 (2002)

A lens group moved in the movable lens unit may either be one lens groupor be of the structure wherein a plurality of lens groups are movedwhile housing therein a plurality of actuators. Or, it is also possibleto arrange a structure wherein one lens group is moved by pluralactuators each having a different response frequency range.

When using a movable lens unit having a lens group capable of beingmoved in the optical axis direction by an actuator, as asphericalalaberration correcting means, it is possible to correct properly thespherical aberration caused by a difference between t1 and t3 by movingthe movable lens group so that magnification m3 of the light-convergingelement for the third light flux λ may satisfy expression (177), asshown in the invention described in Item 261.

Although the optical pickup device of the invention can be applied alsoto the structure wherein three light sources each having a differentwavelength are arranged separately, if there is used a light sourcewherein at least two light sources among three light sources areintegrated solidly as shown in the invention in Item 263, it isadvantageous for downsizing of the optical pickup device and for costreduction. In particular, it is preferable to use a light source whereinall of three light sources are integrated solidly as shown in theinvention in Item 264. As a light source wherein these plural lightsources are integrated solidly, there may be used either a light source(so-called, one-chip laser) wherein emitting points of respective lightsources are formed on one semiconductor chip or a light source(so-called, one-can laser) wherein each light source is housed in onecasing. Or a light source module wherein a light source in which aplurality of light sources are integrated and a photodetector arefurther integrated solidly can also be used.

According to the present invention, an optical element for the opticalpickup device by which the recording and/or reproducing of theinformation can be adequately conducted for a plurality of kinds ofoptical information recording media whose using wavelength is different,including the high density optical disk and DVD using the blue violetlaser light source, aberration correcting element for the optical pickupdevice, light converging element for the optical pickup device,objective optical system, optical pickup device, and optical informationrecording reproducing device, can be obtained.

Initially, the action of the superposition type diffractive structure inthe present invention will be described by taking an example.

An example of the superposition type diffractive structure included inthe optical element of the present invention is shown in FIGS. 9-11. InFIGS. 9-11, the superposition type diffractive structure has a structurein which the saw-toothed shape ring-shaped zone structure (diffractionrelief surface) is divided like a plurality of steps, and in thisexample, each of adjoining steps is formed in such a manner that, in theshortest wavelength and the longest wavelength, the optical pathdifference is generated by integer times of each wavelength and thephase difference is not practically generated.

When the stepped section amount per one step is Δ, aimed-at wavelengthis λ, and refractive index of the medium constituting the steppedsection at this wavelength is n, because the optical path differencegenerated by this stepped section is expressed by Δ(n−1), when thestepped section amount Δ is determined so as to satisfy Δ(n−1)=jλ1, inthis wavelength, the optical path difference is generated byj(integer)-times of the wavelength λ1. Further, when furthermorewavelength is λ3, integers j, k so as to satisfy jλ1≈kλ3 are selected,and the stepped section amount Δ is set so as to satisfy Δ(n−1)=jλ1=kλ3,by this stepped section, because the optical path difference isgenerated by j-times of wavelength for the wavelength λ1, and theoptical path difference is generated by k-times of wavelength for thewavelength λ3, for these 2 wavelengths λ1 and λ3, the wave-fronts arepractically uniform, and the phase difference is not generated.

For example, in the case where λ1=405 nm, λ3=785 nm, because, when j=2,K=1 are selected (that is, stepped section amount Δ=2×405/(n−1)),2×405≈1×785, in this stepped section, in the wavelength λ1=405 nm, theoptical path difference for 2 wavelengths is generated as shown in FIG.9, and in λ3=785 nm, the optical path difference for about onewavelength is generated as shown in FIG. 10. In the structure in which aplurality of such stepped sections are collected, as for wavelengths ofλ1 and λ3, because phases are uniform, no action is generated on thetransmission light.

However, as for the light of the wavelength λ2=655 nm which is differentfrom λ1 and λ3, because the optical path difference of δ=2×405(1.5066−1)/(1.5247−1)−655=127 nm is generated per one stepped section,(herein, 1.5247 is, as will be described later, a refractive index ofthe optical element raw material to the wavelength λ1, and 1.5066 is arefractive index of the optical element raw material to the wavelengthλ2), and when the relief structure of almost saw-toothed shape of onepitch is divided by 4 stepped sections (that is, one pitch is divided by5), the optical path difference for one wavelength of the wavelength λ2is generated (127×5=635 1×655), and as shown in FIG. 11, the wave-frontsof adjoining pitches are overlapped by respectively shifting by 1wavelength. That is, +1-degree diffracted light ray is generated.

As shown in FIG. 11, wave-fronts of adjoining pitches are overlapped byrespectively shifting by 1 wavelength. That is, +1-degree diffractedlight ray is generated.

The m-degree diffraction efficiency ηm by this superposition typediffractive structure is expressed by the following expressions (arith-3and arith-4) when the number of discontinuous stepped sections includedin one pitch is N, height of the stepped section per one step is A,wavelength is λ, and refractive index of the optical element rawmaterial is n.

$\begin{matrix}{{\eta \; m} = \lbrack {\frac{\sin \{ {\pi ( {m - \varphi} )} \}}{\pi \; m}\frac{\sin ( {\pi \; {m/( {N + 1} )}} )}{\sin \{ {{\pi ( {m - \varphi} )}/( {N + 1} )} \}}} \rbrack^{2}} & ( {{Arith}\text{-}3} ) \\{\varphi = \frac{\Delta \; ( {n - 1} )( {N + 1} )}{\lambda}} & ( {{Arith}\text{-}4} )\end{matrix}$

When calculation is conducted for the above example, for λ1, λ3, theyare not diffracted, that is, 0-degree diffracted light ray is generated,and their diffraction efficiencies are respectively 100%, 99.6%, and forλ2, the diffraction efficiency of +1-degree diffracted light ray is87.2%.

Hereupon, in the above calculation, as an optical element raw material,a plastic material in which the refractive index nd on d-line is 1.5091,and Abbe's number νd is 56.5, is assumed, and the refractive index ofthe optical element raw material to λ1, is 1.5247, refractive index ofthe optical element raw material to λ2, is 1.5066, and refractive indexof the optical element raw material to λ3, is 1.5050.

As can be seen from this expression, when the number of stepped sectionsis increased, only left fractional expression in [ ] is remained, andright one gradually approaches 1, and the expression by which thediffraction efficiency of normal saw-toothed diffraction element isgiven, can be obtained. When N takes a finite value, various actions areconducted. As this action, in the case where λ1=405 nm, λ2=650 nm, andλ3=785 nm, the above example is included, and other than that,combinations as shown in following tables (Table 1-Table 8) areconsidered.

In Tables, as φ, the optical path difference of the superposition typediffractive structure for 1 pitch structured by stepped sections of Nsteps as given by (Arith-4) is expressed in a wavelength unit,inversely, the stepped section amount Δ(N+1) is given by using this φ,as Δ(N+1)=φλ/(n−1). φ in each wavelength is different by the wavelengthbecause the stepped section amount Δ(N+1) is the same. Further, m is thediffraction order in which the diffraction efficiency is maximum, andthe diffraction efficiency at that time is ηm.

Hereupon, the calculation herein is assumed as the optical element rawmaterial, the above plastic material.

TABLE 1 Number of stepped sections N = 3 Stepped section amount for 1pitch Δ (N + 1) = 4.63 μm Diffraction efficiency φ Diffraction order mηm λ1 8.00 0 100% λ2 4.77 +1 69.1% λ3 3.97 0 99.8%

TABLE 2 Number of stepped sections N = 4 Stepped section amount for 1pitch Δ (N + 1) = 6.18 μm Diffraction efficiency φ Diffraction order mηm λ1 10.0 0 100% λ2 5.97 +1 87.2% λ3 4.97 0 99.6%

TABLE 3 Number of stepped sections N = 5 Stepped section amount for 1pitch Δ (N + 1) = 7.72 μm Diffraction efficiency φ Diffraction order mηm λ1 12.0 0 100% λ2 7.16 +1 83.7% λ3 5.96 0 99.5%

TABLE 4 Number of stepped sections N = 6 Stepped section amount for 1pitch Δ (N + 1) = 9.26 μm Diffraction efficiency φ Diffraction order mηm λ1 14.0 0 100% λ2 8.36 +1 60.9% λ3 6.95 0 99.2%

TABLE 5 Number of stepped sections N = 8 Stepped section amount for 1pitch Δ (N + 1) = 12.35 μm Diffraction efficiency φ Diffraction order mηm λ1 18.0 0 100% λ2 10.74 +2 68.2% λ3 8.94 0 98.7%

TABLE 6 Number of stepped sections N = 9 Stepped section amount for 1pitch Δ (N + 1) = 13.89 μm Diffraction efficiency φ Diffraction order mηm λ1 20.0 0 100% λ2 11.94 +2 86.4% λ3 9.93 0 98.4%

TABLE 7 Number of stepped sections N = 10 Stepped section amount for 1pitch Δ (N + 1) = 15.44 μm Diffraction Diffraction φ order m efficiencyηm λ1 22.0 0  100% λ2 13.13 +2 84.7% λ3 10.92 0 98.1%

TABLE 8 Number of stepped sections N = 11 Stepped section amount for 1pitch Δ (N + 1) = 16.98 μm Diffraction efficiency φ Diffraction order mηm λ1 24.0 0 100% λ2 14.32 +2 63.7% λ3 11.92 0 97.8%

As described above, when the stepped section amount Δ, and number ofstepped sections N are adequately set, because only one of 3 wavelengthscan be selectively diffracted, and the other wavelengths are notdiffracted, and can be transmitted as they are, when arrangement of eachring-shaped zone of the superposition type diffractive structure isadequately set, while the spherical aberration generated due to thedifference of the protective layer thickness among 3 kinds of opticaldisks of high density optical disk, DVD, and CD is corrected, the hightransmission factor (diffraction efficiency) can be secured for all of 3wavelengths.

Further, the superposition type diffractive structure of the presentinvention can defer the diffraction order of 3 wavelengths or make thediffraction efficiency extremely small to a specific wavelength, andmake it a flare, and make it not contribute to light-converging, otherthan the action by which, as described above, only one of 3 wavelengthsis selectively diffracted, and other wavelengths are made transmitted asthey are.

For example, as shown in Table 9-Table 10, when the stepped sectionamount Δ, the number of stepped sections N are set, because thediffraction orders of 3 wavelengths can be deferred, the degree offreedom of the optical design work can be increased.

TABLE 9 Number of stepped sections N = 10 Stepped section amount for 1pitch Δ (N + 1) = 14.03 μm Diffraction efficiency φ Diffraction order mηm λ1 20.0 −2 89.6% λ2 11.94 +1 96.1% λ3 9.93 −1 95.8%

TABLE 10 Number of stepped sections N = 11 Stepped section amount for 1pitch Δ (N + 1) = 15.57 μm Diffraction efficiency φ Diffraction order mηm λ1 22.0 −2 91.2% λ2 13.13 +1 92.4% λ3 10.92 −1 95.9%

Further, as shown in Table 11-Table 14, when the stepped section amountΔ, number of stepped sections N are set, the diffraction efficiency canbe made extremely small to a specific wavelength, and it can be made notso as to contribute to the light-converging by making it flare.

TABLE 11 Number of stepped sections N = 3 Stepped section amount for 1pitch Δ (N + 1) = 11.58 μm Diffraction efficiency φ Diffraction order mηm λ1 20.0 0  100% λ2 11.94 0 98.8% λ3 9.93 ±2 39.9%

TABLE 12 Number of stepped sections N = 7 Stepped section amount for 1pitch Δ (N + 1) = 10.13 μm Diffraction efficiency φ Diffraction order mηm λ1 15.0 −1 95.6% λ2 8.95 +1 94.3% λ3 7.45 +2 47.1%

TABLE 13 Number of stepped sections N = 4 Stepped section amount for 1pitch Δ (N + 1) = 9.26 μm Diffraction efficiency φ Diffraction order mηm λ1 15.0 0  100% λ2 8.95 −1 86.9% λ3 7.45 +2 28.9%

TABLE 14 Number of stepped sections N = 5 Stepped section amount for 1pitch Δ (N + 1) = 3.86 μm Diffraction efficiency φ Diffraction order mηm λ1 6.0 0  100% λ2 3.58 −2 37.6% λ3 2.98 ±3 40.5%

In Tables 11-13, to the wavelength λ1 and wavelength λ2, the hightransmission factors not smaller than 85% are secured, and to thewavelength λ3, the diffraction efficiency is extremely lowered and isnot larger than 50%. Further, in Table 14, to the wavelength λ1, thehigh transmission factor (diffraction efficiency) of 100% is secured,and to the wavelength λ2 and wavelength λ3, the diffraction efficiencyis extremely lowered, and is not larger than 50%. When such asuperposition type diffractive structure is applied to the objectiveoptical system which can be commonly used for DVD and CD, a role of adichroic filter by which a specific wavelength is cut off and otherwavelengths are transmitted, can be burdened.

For example, in the case where the numerical apertures of the highdensity optical disk, DVD and CD are different form each other, when oneoptical function surface of the objective optical system is divided into3 optical function areas of the first optical function areacorresponding to within NA of CD (for example, within NA 0.45), thesecond optical function area corresponding to from NA of CD to NA of DVD(for example, NA 0.45-NA 0.60), and the third optical function areacorresponding to from NA of DVD to NA of the high density optical disk(for example, NA 0.60-NA 0.85), and the superposition type diffractivestructure in Tables 11-13 is formed in the second optical function area,only the wavelength of λ3 can be cut off.

Further, when the superposition type diffractive structure in Table 14is formed in the third optical function area, the wavelength of λ2 andwavelength of λ3 can be cut off. In this manner, when the superpositiontype diffractive structure in Tables 11-14 is formed in a specificoptical function area, the simple-structured objective optical systemwhich does not require the aperture limit element of separated member,can be realized.

Hereupon, the structure in above Tables 1-14, is an example of a part ofthe superposition-type diffractive structure optimum for the opticalelement raw material whose using wavelengths λ1, λ2, λ3 are respectively405 nm, 655 nm, 785 nm, and whose refractive indexes to λ1, λ2, λ3 arerespectively 1.5247, 1.5066, 1.5050, and for the case where thewavelengths or optical element raw material, different from them, areused, it is not necessarily the optimum structure. That is, thesuperposition type diffractive structure in the present invention is notlimited to only the structure in Tables 1-14, but various changes arepossible corresponding to using wavelength or the characteristic of theoptical element material.

Next, referring to drawings, the best mode to conduct the presentinvention will be described.

The First Embodiment

FIG. 1 is a view generally showing the structure of the first opticalpickup device PU1 by which the recording/reproducing of the informationcan be adequately conducted also for any one of the high density opticaldisk HD, DVD, and CD. The optical specification of the high densityoptical disk HD is, the wavelength λ1=408 nm, thickness t1 of protectivelayer PL1=0.0875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is, the wavelength λ2=685 nm, thickness t2 ofprotective layer PL2=0.6 mm, numerical aperture NA2=0.60, and theoptical specification of CD is, the wavelength λ3=785 nm, thickness t3of protective layer PL3=1.2 mm, and numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture, is not limited to this.

The optical pickup device PU1 is structured by: an objective opticalsystem OBJ structured by: a module MD1 for the high density optical diskHD in which the blue violet semiconductor laser LD1 which is made toemit light when the recording/reproducing of the information isconducted for the high density optical disk HD, and which projects thelaser light flux of 408 nm, with the optical detector PD1 areintegrated; the first light emitting point EP1 which is made to emitlight when the recording/reproducing of the information is conducted forDVD, and which projects the laser light of 658 nm; the second lightemitting point EP2 which is made to emit light when therecording/reproducing of the information is conducted for CD, and whichprojects the laser light of 785 nm; the first light receiving sectionDS1 which light-receives the reflected light flux from the informationrecording surface RL2 of DVD; the second light receiving section DS2which light-receives the reflected light flux from the informationrecording surface RL3 of CD; a laser module LM1 for DVD/CD structured bya prism PS; an aberration correcting element L1; a light convergingelement L2 which has a function by which the laser light fluxestransmitted this aberration correcting element L1, are light convergedon the information recording surfaces RL1, RL2, RL3, and whose bothsurfaces are aspherical surfaces; 2-axes actuator AC; a stop STOcorresponding to numerical aperture NA 0.85 of the high density opticaldisk HD; a polarized beam splitter BS; and a collimator lens COL.

Hereupon, as a light source for the high density optical disk HD, otherthan the above-described blue violet semiconductor laser LD1, a blueviolet SHG laser can also be used.

In the optical pickup device PU1, when the recording/reproducing of theinformation is conducted for the high density optical disk, as its rayof light path is drawn by solid line in FIG. 1, a module MD1 for thehigh density optical disk HD is actuated and the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is made almostparallel light flux through the collimator lens COL, and after ittransmits the polarized beam splitter BS, its light flux diameter isregulated by a stop STO, and it becomes a spot formed on the informationrecording surface RL1 through the protective layer PL1 of the highdensity optical disk HD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing or tracking by the2-axes actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL1 becomes a converging light flux, after passing again the objectiveoptical system OBJ, stop STO, polarized beam splitter BS, and collimatorlens COL, and is converged on the light receiving surface of the lightdetector PD1 of the module MD1 for the high density optical disk HD.Then, by using the output signal of the light detector PD1, theinformation recorded in the high density optical disk HD can be read.

Further, in the optical pickup device PU1, in the case where therecording/reproducing of the information is conducted for DVD, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1, as its ray of lightpath is drawn by a wave line in FIG. 1, is reflected by the prism PS,and after it is reflected by the polarized-beam splitter BS, it becomesa spot formed on the information recording surface RL2 through theprotective layer PL2 of DVD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing or tracking by the2-axes actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL2, transmits again the objective optical system OBJ, and after it isreflected by the polarized beam splitter BS, it is reflected by 2 timesinside the prism PS and is light converged in the light receivingsection DS1. Then, by using the output signal of the light receivingsection DS1, the information recorded in DVD can be read.

Further, in the optical pickup device PU1, in the case where therecording/reproducing of the information is conducted for CD, the secondlight emitting point EP2 is made to emit light. The divergent light fluxprojected from the second light emitting point EP2, as its ray of lightpath is drawn by a two-dot chain line in FIG. 1, is reflected by theprism PS, and after it is reflected by the polarized beam splitter BS,it becomes a spot formed on the information recording surface RL1through the protective layer PL1 of CD by the objective optical systemOBJ. The objective optical system OBJ conducts the focusing or trackingby the 2-axes actuator arranged in its periphery. The reflected lightflux modulated by the information pit on the information recordingsurface RL1, transmits again the objective optical system OBJ, and afterit is reflected by the polarized beam splitter BS, it is reflected by 2times inside the prism PS and is light converged in the light receivingsection DS2. Then, by using the output signal of the light receivingsection DS2, the information recorded in CD can be read.

Next, a structure of the objective optical system will be described. Theaberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, and the refractive index to λ3is 1.5050. Further, the light converging element L2 is a plastic lens,in which the refractive index nd on d-line is 1.5435, and Abbe's numberνd is 56.3. Further, in the periphery of respective optical functionsections (areas of the aberration correcting element L1 and lightconverging element L2 through which the laser light flux from the blueviolet semiconductor laser LD1 passes), flange sections FL1, FL2integrally molded with the optical function section are provided, andwhen both of a part of such flange sections FL1, FL2 are mutuallyconnected together, they are integrated.

Hereupon, when the aberration correcting element L1 and light convergingelement L2 are integrated, both may also be integrated through aconnection member of separated member.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, as shown in FIG. 2,divided into the first optical function area AREA 1 including theoptical axis corresponding to an area of the numerical aperture 0.45 ofCD, the second optical function area AREA 2 corresponding to an areafrom the numerical aperture 0.45 of CD to the numerical aperture 0.60 ofDVD, and the third optical function area AREA 3 corresponding to an areafrom the numerical aperture 0.60 of DVD to the numerical aperture 0.85of the high density optical disk HD, and the superposition typediffractive structures HOE1, HOE2, HOE3, which are structures in which aplurality of ring-shaped zones inside of which the step structure isformed, are arranged around the optical axis, are respectively formed inthe first optical function area AREA 1, second optical function areaAREA 2, and third optical function area AREA 3.

In the superposition type diffractive structure HOE1 formed in the firstoptical function area AREA 1, the depth d31 of the step structure formedin each ring-shaped zone is set to a value calculated by d31=2 λ1/(n−1)(μm), and the number of stepped sections N is set to 4. However, λ1 is awavelength in which the wavelength of the laser light flux projectedfrom the blue violet semiconductor laser LD1 is expressed in micronunit, (herein, λ1=0.408 μm), and n is a refractive index of theaberration correcting element L1 to the wavelength λ1. On the stepstructure in which the depth in the optical axis direction is set insuch a manner, when the laser light flux of the wavelength λ1 enters,between adjoining step structures, the optical path difference of 2×λ1(μm) is generated, and because, to the laser light flux of thewavelength λ1, the phase difference is not practically given, it passesas it is. Hereupon, in the following description, the light flux towhich the phase difference is not practically given by the superpositiontype diffractive structure and which passes as it is, is called as the0-degree diffracted light ray.

Further, on this step structure, the laser light flux of the wavelengthλ3 (herein, λ3=0.785 μm) from the second light emitting point EP2enters, between adjoining step structures, the optical path differenceof (2×λ1/λ3)×λ3 (μm) is generated. Because λ3 is about 2 times of λ1,between adjoining step structures, the optical path difference of about1×λ3 (μm) is generated, and because also to the laser light flux of thewavelength λ3, in the same manner as the laser light flux of thewavelength λ1, the optical path difference is not practically given, itis not diffracted, and passes as it is (0-degree diffracted light ray).

On the one hand, when the laser flux of the wavelength λ2 (herein,λ2=0.658 μm) from the second light emitting point EP2 enters into thisstep structure, because the number of stepped sections N in eachring-shaped zone is set to 4, to the light flux of wavelength λ2, thephase difference is given corresponding to an incident portion of thesuperposition type diffractive structure HOE1 and it is diffracted in+1-degree direction (+1-degree diffracted light ray). The diffractionefficiency of +1-degree diffracted light ray of the laser light flux ofwavelength λ2 in this case, is 87.5%, and it is sufficient light amountfor the recording/reproducing of the information for DVD.

The width Λ1 of each ring-shaped zone of the superposition typediffractive structure HOE1, and the inclination direction (in FIG. 1,the inclination direction of envelope 11 of each step structure) of eachring-shaped zone are set in such a manner that, because, when the laserlight flux of wavelength λ2 enters, the spherical aberration in the overcorrection direction is added to +1-degree diffracted light ray by thediffraction action. The magnification m3 to the wavelength λ3 of theobjective optical system OBJ is determined so that the sphericalaberration due to the difference of thickness between the protectivelayer PL1 of the high density optical disk HD and the protective layerPL3 of CD is corrected, therefore, as the present embodiment, when themagnification m2 to the wavelength λ2 and the magnification m3 to thewavelength λ3 are almost the same, the spherical aberration due to thedifference of thickness between the protective layer PL1 of the highdensity optical disk HD and the protective layer PL2 of DVD is tooover-corrected, and the spherical aberration of laser light flux ofwavelength λ2 transmitted the objective optical system OBJ and theprotective layer PL2 of DVD is under-correction direction.

Herein, the width Λ1 of each ring-shaped zone off the superposition typediffractive structure HOE1, and the inclination direction of eachring-shaped zone are set so that, when the laser light flux ofwavelength λ2 enters into the superposition type diffractive structureHOE1, the spherical aberration amount of the over-correction directionwhich is added to the +1-degree diffracted light ray by the diffractionaction, and the spherical aberration of the under-correction directiongenerated due to a case where the magnification m2 to the wavelength λ2and the magnification m3 to the wavelength λ3 are made almost the same,are cancelled each other. Hereby, the laser light flux of wavelength λ2which transmits the superposition type diffractive structure HOE1 andthe protective layer PL2 of DVD, forms a good spot on the informationrecording surface RL2 of DVD.

Further, in the superposition type diffractive structure HOE2 formed inthe second optical function area AREA 2, the depth d32 of the stepstructure formed in each ring-shaped zone is set to a value calculatedby d32=3 λ1/(n−1) (μm), and the stepped section number N in eachring-shaped zone is set to 4.

When the laser light flux of wavelength λ1 enters into the stepstructure in which the depth of the optical axis direction is set inthis manner, the optical path difference of 3×λ1 (μm) is generatedbetween adjoining step structures, and to the laser light flux ofwavelength λ1, because the phase difference is not practically given, itis not diffracted and passes as it is (0-degree diffracted light ray).

Further, when the laser light flux of wavelength λ2 from the first lightemitting point EP1 enters into this step structure, because the steppedsection number N in each ring-shaped zone is set to 4, to the laserlight flux of wavelength λ2, the phase difference is given correspondingto a part of the superposition type diffractive structure HOE2 on whichthe light flux enters, and it is diffracted to −1-degree direction(−1-degree diffracted light ray). The diffraction efficiency of −1-orderdiffracted light ray of the laser light flux of wavelength λ2 at thistime, is 87.5%, and it is a sufficient light amount for therecording/reproducing of the information for DVD.

Herein, the width Λ2 of each ring-shaped zone of the superposition typediffractive structure HOE2, and the inclination direction of eachring-shaped zone are set so that when the laser light flux of wavelengthλ2 enters into the superposition type diffractive structure HOE2, thespherical aberration of the over correction direction added to −1-degreediffracted light ray by the diffraction action, and the sphericalaberration of under correction direction generated due to a case wherethe magnification m2 to wavelength λ2 and the magnification m3 towavelength λ3 are made almost the same, are cancelled each other.Hereby, the laser light flux of wavelength λ2 which transmits thesuperposition type diffractive structure HOE2 and the protective layerPL2 of DVD, forms a good spot on the information recording surface RL2of DVD.

On the one hand, when the laser light flux of wavelength λ3 from thesecond light emitting point EP2 enters into this step structure, thephase difference is given to the laser light flux of the wavelength λ3corresponding to a part of the superposition type diffractive structureHOE2 on which the light flux enters, and it is diffracted in −2-degreedirection (−2-degree diffracted light ray). In this case, thediffraction efficiency of −2-degree diffracted light ray of the laserlight flux of wavelength λ3, is 24.9% and extremely low.

Hereupon, when the laser light flux of wavelength λ3 enters into thesuperposition type diffractive structure HOE2, other than the above−2-degree diffracted light ray, +2-degree diffracted light ray and+3-degree diffracted light ray are also generated, however, theirdiffraction efficiencies are respectively 23.1%, 11.1%, and lower thanthe diffraction efficiency of −2-degree diffracted light ray.

In the above description, to correct the spherical aberration of theabove under correction direction generated due to a case where themagnification m2 to the wavelength λ2 and the magnification m3 to thewavelength λ3 are made almost the same, the superposition typediffractive structures HOE1 and HOE2 are made structures which generatethe spherical aberration of over correction direction when the laserlight flux of the wavelength λ2 enters, however, structures in which thediffraction powers of superposition type diffractive structure HOE1 andHOE2 are set so as to be positive, and when the laser light flux ofwavelength λ2 enters, the divergent degree of the laser light flux ofwavelength λ2 is made small, and it is projected, may also be formed.

In this case, in the laser light fluxes of wavelength λ2 incident on thesuperposition type diffractive structures HOE1 and HOE2, the divergentdegree becomes small, and they are projected. Because, for the lightconverging element L2, this corresponds to a case where themagnification is increased, to the laser light flux of wavelength λ2incident on the light converging element L2, by this magnificationchange, the spherical aberration of the over correction direction isadded. The widths A1, A2 between respective of ring-shaped zones ofsuperposition type diffractive structures HOE1 and HOE2, and theinclination direction of each ring-shaped zone are determined so thatthe spherical aberration of this over correction direction, and thespherical aberration of the under correction direction generated due toa case where the magnification m2 to the wavelength λ2 and themagnification m3 to the wavelength λ3 are made almost the same, arecancelled.

Further, in the superposition type diffractive structure HOE23 formed inthe third optical function area AREA 3, the depth d33 of the stepstructure formed in each ring-shaped zone is set to a value calculatedby d33=1 λ1) (μm), and the stepped section number N in each ring-shapedzone is set to 5.

When the laser light flux of wavelength λ1 enters into the stepstructure whose depth in the optical axis direction is set in thismanner, the optical path difference of 1×λ1 (μm) is generated betweenadjoining step structures, and because the phase difference is notpractically given to the laser light flux of wavelength λ1, it is notdiffracted, and passes as it is (0-degree diffracted light ray).

On the one hand, when the laser light flux of wavelength λ2 from thefirst light emitting point EP1 enters into this step structure, to thelaser light flux of wavelength λ2, the phase difference is givencorresponding to a part of the superposition type diffractive structureHOE3 on which the light flux enters, and it is diffracted in −2-degreedirection (−2-degree diffracted light ray). The diffraction efficiencyof −2-degree diffracted light ray of the laser light flux of wavelengthλ2 in this time is 39.1% and extremely low. Hereupon, when the laserlight flux of wavelength λ2 enters into the superposition typediffractive structure HOE3, other than the above −2-degree diffractedlight ray, ±3-degree diffracted light ray is also generated, however,this diffraction efficiency is 11.0%, and is further lower than thediffraction efficiency of the −2-degree diffracted light ray. That is,because the superposition type diffractive structure HOE3 actuates thesame work as a dichroic filter by which the laser light flux ofwavelength λ2 is selectively cut off, in the first optical pickup devicePU1, it is not necessary that the aperture limit element to DVD ismounted separately, and the simple structure can be structured.

Further, when the laser light flux of wavelength λ3 from the secondlight emitting point EP2 enters into this step structure, to the laserlight flux of wavelength λ3, the phase difference is given correspondingto a part of the superposition type diffractive structure HOE3 on whichthe light flux enters, and it is diffracted in ±3-degree direction(±3-degree diffracted light ray). The diffraction efficiency of±3-degree diffracted light ray of the laser light flux of wavelength λ3in this time is 40.5% and extremely low. That is, the above-describedsuperposition type diffractive structure HOE2 and the superposition typediffractive structure HOE3 actuate the same work as a dichroic filter bywhich the laser light flux of wavelength λ3 is selectively cut off, inthe first optical pickup device PU1, it is not necessary that theaperture limit element to CD is mounted separately, and the simplestructure can be structured.

Further, the optical function surface S2 on the optical disk side of theaberration correcting element L1 is, as shown in FIG. 2, divided intothe fourth optical function area AREA 4 including the optical axiscorresponding to an area in numerical aperture 0.60 of DVD, and thefifth optical function area AREA 5 corresponding to an area from thenumerical aperture 0.60 to the numerical aperture 0.85 of the highdensity optical disk HD, and the diffractive structures DOE1, DOE2structured by a plurality of ring-shaped zones including the opticalaxis, whose sectional shape is the saw-toothed shape, are respectivelyformed in the optical function area AREA 4 and the optical function areaAREA 5.

The diffractive structures DOE1, DOE2 are structures for suppressing thechromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration change following the incidentwavelength change.

In the diffractive structure DOE1, the height d01 of the stepped sectionclosest to the optical axis is designed so that the diffractionefficiency is 100% to the light flux of wavelength 390 nm (therefractive index of the aberration correcting element L1 to thewavelength 390 nm, is 1.5273), and satisfies the above-describedexpression (16). Because, on the diffractive structure DOE1 in which adepth of the stepped section is set in this manner, when the laser lightflux of wavelength λ1 enters, +2-degree diffracted light ray isgenerated in the diffraction efficiency of 96.8%, when the laser lightflux of wavelength λ2 enters into it, +1-degree diffracted light ray isgenerated in the diffraction efficiency of 93.9%, and when the laserlight of wavelength λ3 enters into it, +1-degree diffracted light ray isgenerated in the diffraction efficiency of 99.2%, in any wavelengtharea, the sufficient diffraction efficiency can be obtained, and evenwhen the chromatic aberration is corrected in the blue violet area, thechromatic aberration correction in the wavelength areas of thewavelength λ2 and wavelength λ3 is not too surplus.

On the one hand, because the diffractive structure DOE2 is optimized forthe wavelength λ1, when the laser light flux of the wavelength λ1 entersinto the diffractive structure DOE2, +2-degree diffraction light isgenerated in the diffraction efficiency of 100%.

Further, the diffractive structures DOE1, DOE2 has the wavelengthdependency of the spherical aberration in which, in the blue violetarea, when the wavelength of incident light flux is increased, thespherical aberration changes in the under correction direction, and whenthe wavelength of the incident light flux is reduced, the sphericalaberration changes in the over correction direction. Hereby, because thespherical aberration change generated in the light converging elementfollowing the incident wavelength change is cancelled, the regulationfor the oscillation wavelength of the blue violet semiconductor laserLD1 can be softened.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source, and type diffractive structure is formed on the opticalfunction surface S2 on the optical disk side, is applied, in contrast tothis, a structure in which the type diffractive structure is formed onthe optical function surface S1 on the semiconductor laser light sourceside, and the superposition type diffractive structure is formed on theoptical function surface S2 on the optical disk side, may also beapplied.

The Second Embodiment

FIG. 3 is a view generally showing a structure of the second opticalpickup device PU2 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density optical diskHD, DVD and CD. The optical specification of the high density opticaldisk is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.0875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.67, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU2 is structured by: a laser module LM2 forthe high density optical disk HD/DVD structured by the first lightemitting point EP1 which is made to emit light when therecording/reproducing of the information is conducted for the highdensity optical disk HD, and which projects the laser light flux of 408nm, the second light emitting point EP2 which is made to emit light whenthe recording/reproducing of the information is conducted for DVD, andwhich projects the laser light flux of 658 nm, the first light receivingsection DS1 which light-receives the reflected light flux from theinformation recording surface RL1 of the high density optical disk HD,the second light receiving section DS2 which light-receives thereflected light flux from the information recording surface RL2 of DVD,and a prism PS; a module MD2 for CD in which the infrared semiconductorlaser LD3 which is made to emit light when the recording/reproducing ofthe information is conducted for CD, and which projects the laser lightflux of 785 nm, and the light detector PD3 are integrated; objectiveoptical system CBJ structured by an aberration correcting element L1 anda light converging element L2 having a function by which the laser lightflux transmitted this aberration correcting element L1 islight-converged on the information recording surfaces RL1, RL2, RL3, andboth surfaces of which are aspherical surfaces; 2-axis actuator AC; stopSTO corresponding to numerical aperture NA 0.85 of the high densityoptical disk HD; polarized beam splitter BS; collimator lens COL; andcoupling lens CUL.

In the optical pickup device PU2, when the recording/reproducing of theinformation is conducted for the high density optical disk, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1 is, as the ray oflight path is drawn by a solid line in FIG. 3, reflected by the prismPS, and via the collimator lens COL, after it is made almost parallellight flux, it transmits the polarized beam splitter, the light fluxdiameter is regulated by the stop STO, and it becomes a spot formed onthe information recording surface RL1 through the protective layer PL1of the high density optical disk by the objective optical system OBJ.The objective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL1 is, after it transmits again the objective optical system OBJ, stepSTO, polarized beam splitter BS, it is made the converged light flux bythe collimator lens COL, and reflected by 2 times inside the prism PS,and light-converged in the light receiving section DS1. Then, by usingthe output signal of the light receiving section DS1, the informationrecorded in the high density optical disk HD can be read.

Further, in the optical pickup device PU2, when therecording/reproducing of the information is conducted for DVD, thesecond light emitting point EP2 is made to emit light. The divergentlight flux projected from the second light emitting point EP2 is, as theray of light path is drawn by a dotted line in FIG. 3, reflected by theprism PS, and via the collimator lens COL, after it is made almostparallel light flux, it transmits the polarized beam splitter, and itbecomes a spot formed on the information recording surface RL2 throughthe protective layer PL2 of the DVD by the objective optical system OBJ.The objective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surface R2is, after it transmits again the objective optical system OBJ, polarizedbeam splitter BS, it is made the converged light flux by the collimatorlens COL, and reflected by 2 times inside the prism PS, andlight-converged in the light receiving section DS2. Then, by using theoutput signal of the light receiving section DS2, the informationrecorded in DVD can be read.

Further, when the recording/reproducing of the information is conductedfor CD, as the ray of light path is drawn by a two-dot chain line inFIG. 3, the module MD2 for CD is actuated, and the infraredsemiconductor laser LD3 is made to emit light. The divergent light fluxprojected from the infrared semiconductor laser LD3 is, after thedivergent angle is converted by the coupling lens CUL, reflected by thepolarized beam splitter BS, and it becomes a spot formed on theinformation recording surface RL3 through the protective layer PL3 of CDby the objective optical system OBJ. The objective optical system OBJconducts the focusing and tracking by 2-axis actuator AC arranged in itsperiphery. The reflected light flux modulated by the information pit onthe information recording surface RL3 is, after it transmits again theobjective optical system OBJ, it is reflected by the polarized beamsplitter BS, and the divergent angle is converted by the coupling lensCUL, and converged on the light receiving surface of the light detectorPD3 of the module MD2 for CD. Then, by using the output signal of thelight detector PD3, the information recorded in CD can be read.

Next, a structure of the objective optical system will be described. Theaberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, and the refractive index to λ3is 1.5050. Further, the light converging element L2 is a plastic lens,in which the refractive index nd on d-line is 1.5435, and Abbe's numberνd is 56.3. Further, in the periphery of respective optical functionsections (areas of the aberration correcting element L1 and lightconverging element L2 through which the laser light flux from the blueviolet semiconductor laser LD1 passes), flange sections FL1, FL2integrally molded with the optical function section are provided, andwhen both of a part of such flange sections FL1, FL2 are mutuallyconnected together, they are integrated.

Hereupon, when the aberration correcting element L1 and light convergingelement L2 are integrated, both may also be integrated through aconnection member of separated member.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, as shown in FIG. 4,divided into the sixth optical function area AREA 6 including theoptical axis corresponding to an area in the numerical aperture 0.67 ofDVD, and the seventh optical function area AREA 7 corresponding to anarea from the numerical aperture 0.67 of DVD to the numerical aperture0.85 of the high density optical disk, and in the sixth optical functionarea AREA 6, the superposition type diffractive structures HOE4, whichis a structure in which a plurality of ring-shaped zones inside of whichthe step structure is formed, are arranged around the optical axis, isformed. In the superposition type diffractive structures HOE4 formed inthe sixth optical function area AREA 6, the depth d34 of step structureformed in each ring-shaped zone is set to a value calculated by d34=2λ1/(n−1) (μm), and the stepped section number N in each ring-shaped zoneis set to 4. Where, λ1 is the wavelength of the laser light fluxprojected from the blue violet semiconductor laser LD1 is expressed in amicron unit, (herein, λ1=0.408 μm), and n is a refractive index to thewavelength λ1 of the aberration correcting element L1.

When the laser light flux of wavelength λ1 from the first light emittingpoint EP1 enters into the step structure whose depth in the optical axisdirection is set in such a manner, the optical path difference of 2×λ1(μm) is generated between adjoining step structures, and to the laserlight flux of wavelength λ1, because the phase difference is notpractically given, it is not diffracted and transmits as it is (0-degreediffracted light ray).

Further, when the laser light flux of the wavelength λ3 (herein,λ3=0.785 μm) enters into this step structure, because the wavelength λ3is about 2 times of λ1, the optical path difference of 1×λ3 (μm) isgenerated between adjoining step structures, and in the same manner asthe laser light flux of λ1, also to the laser light flux of wavelengthλ3, because the phase difference is not practically given, it is notdiffracted, and transmits as it is (0-degree diffracted light ray).

On the one hand, when the laser light flux of the wavelength λ2 (herein,λ2=0.658 μm) from the second light emitting point EP2 enters into thisstep structure, because the stepped section number in each ring-shapedzone is set to 5, to the laser light flux of λ2, the phase difference isgiven corresponding to a part on which the light flux enters, of thesuperposition type diffractive structure HOE1, and the laser light fluxis diffracted in +1-degree direction (+1-degree diffracted light ray).The diffraction efficiency of +1-degree diffracted light ray at thistime is 87.5%, and it is a light amount sufficient for therecording/reproducing of the information for DVD.

The width Λ4 of each ring-shaped zone of the superposition typediffractive structure HOE4, and the inclination direction of eachring-shaped zone (in FIG. 3, the inclination direction of the envelop 14of each step structure) are set so that, when the laser light flux ofwavelength λ2 enters, the spherical aberration of under correctiondirection is added to +1-degree diffracted light ray by the diffractionaction.

The objective optical system OBJ is designed in such a manner that, to acombination of the wavelength λ1, magnification m1=0, and the protectivelayer PL1 of the high density optical disk HD, the spherical aberrationbecomes minimum. Therefore, as in the present embodiment, when themagnification m1 to the laser light flux of wavelength λ1, and themagnification m2 to the laser light flux of wavelength λ2, are madealmost the same, due to the difference of the thickness between theprotective layer PL1 of the high density optical disk and the protectivelayer PL2 of DVD, the spherical aberration of the laser light flux ofthe wavelength λ2 transmitted the objective optical system OBJ and theprotective layer PL2 of DVD, is in the over correction direction.

Herein, the width Λ4 of each ring-shaped zone of the superposition typediffractive structure HOE4, and the inclination direction of eachring-shaped zone are set so that, when the laser light flux ofwavelength λ2 enters into the superposition type diffractive structureHOE4, the spherical aberration of the under correction direction addedto +1-degree diffracted light ray by the diffraction action, and thespherical aberration of over correction direction generated due to acase where the magnification m1 to wavelength λ1 and the magnificationm2 to wavelength λ2 are made almost the same, are cancelled each other.Hereby, the laser light flux of wavelength λ2 which transmits thesuperposition type diffractive structure HOE4 and the protective layerPL2 of DVD, forms a good spot on the information recording surface RL2of DVD.

In the above description, to correct the spherical aberration of theover correction direction generated due to a case where themagnification m1 to the wavelength λ1 and the magnification m2 to thewavelength λ2 are made almost the same, the superposition typediffractive structure HOE4 is made a structure in which, when the laserlight flux of wavelength λ2 enters, the spherical aberration of theunder correction direction is generated, however, a structure in whichthe diffraction power of the superposition type diffractive structureHOE4 is set so as to be negative, and when the laser light flux ofwavelength λ2 enters, the divergent degree of the laser light flux ofwavelength λ2 is increased, and it is projected, may also be applied.

In this case, in the laser light flux of wavelength λ2 incident on thesuperposition type diffractive structure HOE4, its divergent degree isincreased and it is projected. Because this corresponds to a case wherethe magnification is reduced, for the light converging element L2, tothe laser light flux of the wavelength λ2 incident on the lightconverging element L2, the spherical aberration in the under correctiondirection is added by this magnification change. The width Λ4 betweeneach of ring-shaped zones of the superposition type diffractivestructure HOE4 and the inclination direction of each ring-shaped zoneare determined so that this spherical aberration of under correctiondirection and the spherical aberration of the over correction directiongenerated due to a case where the magnification m1 to the wavelength λ1and the magnification m2 to λ2 are made almost the same, are cancelled.

Further, the optical function surface S2 on the optical disk side of theaberration correcting element L1 is, as shown in FIG. 4, divided intothe eighth optical function area AREA 8 including the optical axiscorresponding to an area in numerical aperture 0.67 of DVD, and theninth optical function area AREA 9 corresponding to an area from thenumerical aperture 0.67 to the numerical aperture 0.85 of the highdensity optical disk HD, and the diffractive structures DOE3, DOE4structured by a plurality of ring-shaped zones including the opticalaxis, whose sectional shape is the saw-toothed shape, are respectivelyformed in the optical function area AREA 8 and the optical function areaAREA 9.

The diffractive structures DOE3, DOE4 are structures for suppressing thechromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration change following thetemperature change.

In the diffractive structure DOE3, the height d03 of the stepped sectionclosest to the optical axis is designed so that the diffractionefficiency is 100% to the light flux of wavelength 390 nm (therefractive index of the aberration correcting element L1 to thewavelength 390 nm, is 1.5273), and satisfies the above-describedexpression (16). Because, on the diffractive structure DOE1 in which adepth of the stepped section is set in this manner, when the laser lightflux of wavelength λ1 enters, because +2-degree diffracted light ray isgenerated in the diffraction efficiency of 96.8%, when the laser lightflux of wavelength λ2 enters into it, +1-degree diffracted light ray isgenerated in the diffraction efficiency of 93.9%, and when the laserlight of wavelength λ3 enters into it, +1-degree diffracted light ray isgenerated in the diffraction efficiency of 99.2%, in any wavelengtharea, the sufficient diffraction efficiency can be obtained, and evenwhen the chromatic aberration is corrected in the blue violet area, thechromatic aberration correction in the wavelength areas of thewavelength λ2 and wavelength λ3 is not too surplus.

On the one hand, because the diffractive structure DOE4 is optimized tothe wavelength λ1, when the laser light flux of wavelength λ1 entersinto the diffractive structure DOE4, +2-degree diffracted light ray isgenerated in the diffraction efficiency of 100%.

Further, the diffractive structure DOE3, DOE4 have a wavelengthdependency of the spherical aberration, in the blue violet area, inwhich, when the wavelength of the incident light flux is increased, thespherical aberration changes in the under correction direction, and whenthe wavelength of the incident light flux is reduced, the sphericalaberration changes in over correction direction. Hereby, when thespherical aberration generated in the light converging element followingthe environmental temperature change is cancelled, the temperature rangewhich can be used in the objective optical system OBJ which is a plasticlens of high NA, is spread.

In the aberration correcting element L1 in the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, and the type diffractive structure is formed on theoptical function surface S2 on the optical disk side, is applied,however, in contrast to this, a structure in which the type diffractivestructure is formed on the optical function surface S1 on thesemiconductor laser light source side, and the superposition typediffractive structure is formed on the optical function surface S2 onthe optical disk side, may also be applied.

Further, because the objective optical system OBJ of the presentembodiment, is an optical system in which the sinusoidal condition iscorrected to the infinite object point, it does not satisfy thesinusoidal condition to the finite object point. Therefore, as in thecase where the recording/reproducing of the information is conducted forCD, in the case where the divergent light flux enters into the objectiveoptical system OBJ, when the objective optical system OBJ shifts in thedirection perpendicular to the optical axis (track direction of CD),because the light emitting point of the infrared semiconductor laser LD3becomes an off-axis object point, the coma is generated.

The coupling lens CUL is a coma correcting element having a function forreducing such a coma, and is designed so that, when the objectiveoptical system OBJ is not driven by 2-axis actuator in the directionperpendicular to the optical axis, in the effective diameter throughwhich the laser light flux of wavelength λ3 passes, the sphericalaberration is corrected so as to be less than diffraction limit, andoutside this effective diameter, the spherical aberration is generatedin the over correction direction.

Hereby, when the objective optical system OBJ shifts in the directionperpendicular to the optical axis, because the laser light flux ofwavelength λ3 passes the area designed so that it has large sphericalaberration, the coma is added to the laser light flux of wavelength λ3passed the coupling lens CUL and the objective optical system OBJ. Thedirection and the magnitude of the spherical aberration outside theeffective diameter of the coupling lens CUL are determined so that thiscoma and the coma due to a case where the light emitting point of theinfrared semiconductor laser LD3 is an off-axis object point, arecancelled.

By using in combination with the coupling lens CUL designed in thismanner, the tracking characteristic of the objective optical system OBJfor CD, which does not satisfy the sinusoidal condition to the finiteobject point, can be made good one.

Herein, an aperture switching when the recording/reproducing of theinformation is conducted for DVD and CD, in the second optical pickupdevice PU2 of the present embodiment, will be described.

In the second optical pickup device PU2, because NA1, NA2 and NA3 arerespectively different, when the recording/reproducing of theinformation is conducted for DVD and CD, it is necessary that aperturesare switched corresponding to the numerical aperture of respectiveoptical disks.

Because the superposition type diffractive structure HOE4 is formed inthe optical function area AREA 6 including the optical axis, thespherical aberration to the wavelength λ2 is corrected only for thelight flux passing the sixth optical function area AREA 6, and for thelight flux passing the seventh optical function area AREA 7 surroundingits periphery, it is not corrected. Accordingly, in the light fluxes ofwavelength λ2 incident on the objective optical system OBJ, the lightflux which passes the seventh optical function area AREA 7, becomes aflare component which does not contribute the spot formation onto theinformation recording surface RL2.

Because this is equivalent to a case where the aperture switching isautomatically conducted corresponding to NA2, it is not necessary thatthe aperture limit element corresponding to the numerical aperture NA2of DVD is provided separately, in the second optical pickup device PU2.

On the one hand, because the objective optical system OBJ is notprovided with the aperture switching function to the wavelength λ3, itis necessary that the aperture limit element corresponding to thenumerical aperture NA3 of CD, is provided separately, and in theobjective optical system OBJ, as such an aperture limit element, awavelength selection filter WF is formed on the optical function surfaceS1 on the semiconductor laser light source side of the aberrationcorrecting element L1.

The wavelength selection filter WF has, as shown in FIG. 12, thewavelength selectivity of the transmission factor in which all ofwavelengths of λ1 to λ3 are passed in an area in NA3, and in an area ofthe outside of NA3, only the wavelength λ3 is cut off, and by such awavelength selectivity, the aperture switching corresponding to NA3 isconducted.

Hereupon, to the wavelength selection filter WF, the wavelengthselectivity of transmission factor as shown in FIG. 13, may also begiven. Because this wavelength selection filter WF has the wavelengthselectivity of the transmission factor in which all of wavelengths of λ1to λ3 are passed in an area in NA3, in an area from NA3 to NA2, only thewavelength λ3 is cut off, and in an area from NA2 to NA1, thewavelengths λ2 and λ3 are cut off, by such a wavelength selectivity, theaperture switching corresponding to NA2 and NA3 can be conducted.

Further, in the present embodiment, the wavelength selection filter WFis formed on the optical function surface of the aberration correctingelement L1, however, it may also be formed on the optical functionsurface of the light converging element L2, or an aperture limit elementAP in which such a wavelength selection filter WF is formed on itsoptical function surface, may be mounted separately. In this case, it ispreferable that the aperture limit element AP and the objective opticalsystem OBJ are integrally tracking-driven.

The Third Embodiment

FIG. 5 is a view generally showing a structure of the third opticalpickup device PU3 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.0875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.67, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.51.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU3 is structured by: a laser module LM1 forDVD/CD structured by the module MD1 for high density optical disk HD inwhich the blue violet semiconductor laser LD1 which is made to emitlight when the recording/reproducing of the information is conducted forthe high density optical disk HD and which projects the laser light fluxof 408 nm, and the light detector PD1 are integrated, the first lightemitting point EP1 which is made to emit light when therecording/reproducing of the information is conducted for DVD, and whichprojects the laser light flux of 658 nm, the second light emitting pointEP2 which is made to emit light when the recording/reproducing of theinformation is conducted for CD, and which projects the laser light fluxof 785 nm, the first light receiving section DS1 which light-receivesthe reflected light flux from the information recording surface RL2 ofDVD, the second light receiving section DS2 which light-receives thereflected light flux from the information recording surface RL3 of CD,and a prism PS; the objective optical system OBJ structured by anaberration correcting element L1 and a light converging element L2having a function by which the laser light flux transmitted thisaberration correcting element L1 is light-converged on the informationrecording surfaces RL1, RL2, RL3, and both surfaces of which areaspherical surfaces; 2-axis actuator AC; stop STO corresponding tonumerical aperture NA 0.85 of the high density optical disk HD;polarized beam splitter BS; collimator lens COL; and coupling lens CUL.

Hereupon, as the light source for the high density optical disk HD,other than the above-described blue violet semiconductor laser LD1, ablue violet SHG laser can also be used.

In the optical pickup device PU2, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 5, the module MD1 forthe high density optical disk HD, is actuated and the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is made almostparallel light flux via the collimator lens COL, and after transmits thepolarized beam splitter BS, the light flux diameter is regulated by stopSTO, and it becomes a spot formed on the information recording surfaceRL1 through the protective layer PL1 of the high density optical disk HDby the objective optical system OBJ. The objective optical system OBJconducts the focusing and tracking by 2-axis actuator AC arranged in itsperiphery. The reflected light flux modulated by the information pit onthe information recording surface RL1 is, after it transmits again theobjective optical system OBJ, stop STO, polarized beam splitter BS andcollimator lens COL, it becomes the converged light flux, and isconverged on the light receiving surface of the light detector PD1 ofthe module MD1 for the high density optical disk HD. Then, by using theoutput signal of the light detector PD1, the information recorded in thehigh density optical disk HD can be read.

Further, in the optical pickup device PU3, when therecording/reproducing of the information is conducted for DVD, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1 is, as the ray oflight path is drawn by a wave line in FIG. 5, reflected by the prism PS,and after its divergent angle is converted by the coupling lens CUL, itis reflected by the polarized beam splitter BS, and it becomes a spotformed on the information recording surface RL2 through the protectivelayer PL2 of the DVD by the objective optical system OBJ. The objectiveoptical system OBJ conducts the focusing and tracking by 2-axis actuatorAC arranged in its periphery. The reflected light flux modulated by theinformation pit on the information recording surface RL2 is, after ittransmits again the objective optical system OBJ, and reflected by thepolarized beam splitter BS, the divergent angle is converted by thecoupling lens CUL, and it is reflected by 2 times inside the prism PS,and light-converged in the light receiving section DS1. Then, by usingthe output signal of the light receiving section DS1, the informationrecorded in DVD can be read.

Further, in the optical pickup device PU3, when therecording/reproducing of the information is conducted for CD, the secondlight emitting point EP2 is made to emit light. The divergent light fluxprojected from the second light emitting point EP2 is, as the ray oflight path is drawn by a two-dot chain line in FIG. 5, reflected by theprism PS, and after its divergent angle is converted by the couplinglens CUL, it is reflected by the polarized beam splitter BS, and itbecomes a spot formed on the information recording surface RL1 throughthe protective layer PL1 of the CD by the objective optical system OBJ.The objective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL1 is, after it transmits again the objective optical system OBJ, andreflected by the polarized beam splitter BS, the divergent angle isconverted by the coupling lens CUL, and it is reflected by 2 timesinside the prism PS, and light-converged in the light receiving sectionDS2. Then, by using the output signal of the light receiving sectionDS2, the information recorded in CD can be read.

Next, a structure of the objective optical system OBJ will be described.The aberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 l is 1.5242, the refractive index to λ2is 1.5064, and the refractive index to λ3 is 1.5050. Further, the lightconverging element L2 is a plastic lens, in which the refractive indexnd on d-line is 1.5435, and Abbe's number νd is 56.3. Further, in theperiphery of respective optical function sections (areas of theaberration correcting element L1 and light converging element L2 throughwhich the laser light flux from the blue violet semiconductor laser LD1passes), flange sections FL1, FL2 integrally molded with the opticalfunction section are provided, and when both of a part of such flangesections FL1, FL2 are mutually connected together, they are integrated.

Hereupon, when the aberration correcting element L1 and light convergingelement L2 are integrated, both may also be integrated through aconnection member of separated member.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element. L1 is, as shown in FIG. 6,divided into the tenth optical function area AREA 10 including theoptical axis corresponding to an area in the numerical aperture 0.67 ofDVD, and the eleventh optical function area AREA 11 corresponding to anarea from the numerical aperture 0.67 of DVD to the numerical aperture0.85 of the high density optical disk, and in the tenth optical functionarea AREA 10, the superposition type diffractive structures HOES, whichis a structure in which a plurality of ring-shaped zones inside of whichthe step structure is formed, are arranged around the optical axis, isformed.

In the superposition type diffractive structures HOES formed in thetenth optical function area AREA 10, the depth d35 of step structureformed in each ring-shaped zone is set to a value calculated by d35=2λ1/(n−1) (μm), and the stepped section number N in each ring-shaped zoneis set to 4. Where, λ1 is the wavelength of the laser light flux whichis projected from the blue violet semiconductor laser LD1, and which isexpressed in a micron unit, (herein, λ1=0.408 μm), and n is a refractiveindex to the wavelength λ1 of the aberration correcting element L1.

When the laser light flux of wavelength λ1 enters into the stepstructure whose depth in the optical axis direction is set in such amanner, the optical path difference of 2×λ1 (μm) is generated betweenadjoining step structures, and to the laser light flux of wavelength λ1,because the phase difference is not practically given, it is notdiffracted and transmits as it is (0-degree diffracted light ray).

Further, when the laser light flux of the wavelength λ3 (herein,λ3=0.785 μm) enters into this step structure, because the wavelength λ3is about 2 times of λ1, the optical path difference of 1×λ3 (μm) isgenerated between adjoining step structures, and in the same manner asthe laser light flux of λ1, also to the laser light flux of wavelengthλ3, because the phase difference is not practically given, it is notdiffracted, and transmits as it is (0-degree diffracted light ray).

On the one hand, when the laser light flux of the wavelength λ2 (herein,λ2=0.658 μm) from the second light emitting point EP2 enters into thisstep structure, because the stepped section number N in each ring-shapedzone is set to 5, to the laser light flux of λ2, the phase difference isgiven corresponding to a part on which the light flux enters, of thesuperposition type diffractive structure HOE5, and the laser light fluxis diffracted in +1-degree direction (+1-degree diffracted light ray).The diffraction efficiency of +1-degree diffracted light ray at thistime is 87.5%, and it is a light amount sufficient for therecording/reproducing of the information for DVD.

The width Λ5 of each ring-shaped zone of the superposition typediffractive structure HOE5, and the inclination direction of eachring-shaped zone (in FIG. 5, the inclination direction of the envelop 15of each step structure) are set so that, when the laser light flux ofwavelength λ2 enters, the spherical aberration of under correctiondirection is added to +1-degree diffracted light ray by the diffractionaction.

Further, the minimum value P of the width of the step structure of thesuperposition type diffractive structure HOE5 is set, for the purposethat the metallic molding by SPDT is made easy, and to the wavelength λ1of the blue violet area, the diffraction efficiency lowering by theshape error of the metallic mold is not too large, so as to satisfy theabove expression (9). Therefore, by only the action of superpositiontype diffractive structure HOE5, the spherical aberration in the overcorrection direction, generated due to the thickness of the protectivelayer PL1 of the high density optical disk HD and the protective layerPL2 of DVD can not be corrected.

Accordingly, the magnification m2 to the wavelength λ2 of the objectiveoptical system OBJ is set so that the spherical aberration in the overcorrection direction remained without the correction being enabled, iscorrected. Hereby, the laser light flux of wavelength λ2 transmitted thesuperposition type diffractive structure HOE5 and the protective layerPL2 of DVD, forms a good spot on the information recording surface RL2of DVD.

In the above description, the superposition type diffractive structureHOE5 is made a structure in which, when the laser light flux ofwavelength λ2 enters, the spherical aberration of the under correctiondirection is generated, however, a structure in which the diffractionpower of the superposition type diffractive structure HOE5 is set so asto be negative, and when the laser light flux of wavelength λ2 enters,the divergent degree of the laser light flux of wavelength λ2 isincreased, and it is projected, may also be applied.

In this case, in the laser light flux of wavelength λ2 incident on thesuperposition type diffractive structure HOES, its divergent degree isincreased and it is projected. Because this corresponds to a case wherethe magnification is reduced, for the light converging element Lλ, tothe laser light flux of the wavelength λ2 incident on the lightconverging element L2, the spherical aberration in the under correctiondirection is added by this magnification change. Also in this case, thewidth Λ4 between respective ring-shaped zones of the superposition typediffractive structure HOES and the inclination direction of eachring-shaped zone are determined so that above-described expression (9)is satisfied, and the magnification m2 to the wavelength λ2 of theobjective optical system OBJ is determined so that the sphericalaberration in the over correction direction remained without thecorrection being enabled, is corrected.

Further, the optical function surface S2 on the optical disk side of theaberration correcting element L1 is, as shown in FIG. 6, divided intothe twelfth optical function area AREA 12 including the optical axiscorresponding to an area in numerical aperture 0.67 of DVD, and thethirteenth optical function area AREA 13 corresponding to an area fromthe numerical aperture 0.67 of DVD to the numerical aperture 0.85 of thehigh density optical disk HD, and the diffractive structures DOE5, DOE6structured by a plurality of ring-shaped zones including the opticalaxis, whose sectional shape is the saw-toothed shape, are respectivelyformed in the optical function area AREA 12 and the optical functionarea AREA 13.

The diffractive structures DOE5, DOE6 are structures for suppressing thechromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration change following thetemperature change, and because the specific structure of them is thesame as diffractive structures DOE3, DOE4 of the optical pickup devicePU2, the detailed description is neglected herein.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, and diffractive structure is formed on the opticalfunction surface S2 on the optical disk side, is applied, in contrast tothis, a structure in which the diffractive structure is formed on theoptical function surface S1 on the semiconductor laser light sourceside, and the superposition type diffractive structure is formed on theoptical function surface S2 on the optical disk side, may also beapplied.

Further, the coupling lens CUL is an optical element for the purpose inwhich the divergent angle of the laser light flux of wavelength λ2projected from the first light emitting point EP1 and the divergentangle of the laser light flux of wavelength λ3 projected from the secondlight emitting point EP2, are respectively converted into themagnification m2 to the wavelength λ2 of the objective optical systemOBJ and the magnification m3 to the wavelength λ3, and they areprojected.

The coupling lens CUL is a plastic lens in which the refractive index ndon d-line is 1.5091, and Abbe's number νd is 56.5, and the refractiveindex to the wavelength λ2 is 1.5064, and the refractive index to thewavelength λ3 is 1.5050.

Herein, the paraxial refractive power to the wavelength λ2 is determinedso that the divergent angle of the laser light flux of wavelength λ2projected from the first light emitting point EP1 is converted into thedivergent angle corresponding to the magnification m2 to the wavelengthλ2 of the objective optical system OBJ, and it can be projected.

The optical function surface S2 on the optical disk side of the couplinglens CUL is divided into the fourteenth optical function area AREA 14(graphic display is neglected) including the optical axis correspondingto an area in numerical aperture 0.51 of CD, and the fifteenth opticalfunction area AREA 15 (graphic display is neglected) corresponding to anarea from numeral aperture 0.51 of CD to numeral aperture 0.67 of DVD,and the superposition type diffractive structure HOE6 which is astructure in which a plurality of ring-shaped zones inside of which stepstructure is formed, are arranged around the optical axis, is formed inthe optical function area AREA 14.

In the superposition type diffractive structure HOE6 formed in thefourteenth optical function area AREA 14, the depth d36 of the stepstructure formed in each ring-shaped zone is set to a value calculatedby d36=1 λ2/(n−1) (μm), and the number of stepped sections N is set to5. However, λ2 is a wavelength in which the wavelength of the laserlight flux projected from the first light emitting point EP1 isexpressed in micron unit, and n is a refractive index of the couplinglens CUL to the wavelength λ2. On the step structure in which the depthin the optical axis direction is set in such a manner, when the laserlight flux of the wavelength λ2 enters, between adjoining stepstructures, the optical path difference of 1×λ1 (μm) is generated, andbecause, to the laser light flux of the wavelength λ2, the phasedifference is not practically given, it is not diffracted and it passesas it is (0-degree diffracted light ray).

On the one hand, when the laser light flux of the wavelength λ3 from thesecond light emitting point EP2 enters into this step structure, becausethe stepped section number N in each ring-shaped zone is set to 5, tothe laser light flux of λ3, the phase difference is given correspondingto a part on which the light flux enters, of the superposition typediffractive structure HOE6, and the laser light flux is diffracted in−1-degree direction (−1-degree diffracted light ray). The diffractionefficiency of −1-degree diffracted light ray at this time is 91.1%, andit is a light amount sufficient for the recording/reproducing of theinformation for CD.

The paraxial diffraction power to the wavelength λ3 of the superpositiontype diffractive structure HOE6 is set so as to be negative, and thewidth Λ6 of each ring-shaped zone of the superposition type diffractivestructure HOE6, and the inclination direction of each ring-shaped zone(in FIG. 5, the inclination direction of the envelop 16 of each stepstructure) are determined so that, the divergent angle of the laserlight flux of wavelength λ3 projected from the second light emittingpoint EP2 is converted into the divergent angle corresponding to themagnification m3 to the wavelength λ3 of the objective optical systemOBJ.

In this manner, when the wavelength selectivity of the diffractionaction of the superposition type diffractive structure HOE6 is used,even when the magnification m2 to the wavelength λ2 of the objectiveoptical system OBJ, and the magnification m3 to the wavelength λ3 aredifferent each other, the laser module LM1 for DVD/CD in which the laserlight source for DVD and the laser light source for CD are integrated,can be used.

Herein, the aperture switching when the recording/reproducing of theinformation is conducted for DVD and CD in the third optical pickupdevice PU3 of the present embodiment, will be described.

Because in the third optical pickup device PU3, NA1, NA2 and NA3 arerespectively different, when the recording/reproducing of theinformation is conducted for DVD and CD, it is necessary that,corresponding to numerical apertures of respective optical disks, theaperture is switched.

Because the superposition type diffractive structure HOE5 is formed inthe tenth optical function area AREA 10 including the optical axis, thespherical aberration to the wavelength λ2 is corrected only for thelight flux passing the tenth optical function area AREA 10, and for thelight flux passing the eleventh optical function area AREA 11surrounding its periphery, it is not corrected. Accordingly, in thelight fluxes of wavelength λ2 incident on the objective optical systemOBJ, the light flux which passes the eleventh optical function area AREA11, becomes a flare component which does not contribute the spotformation onto the information recording surface RL2 of DVD.

Because this is equivalent to a case where the aperture switching isautomatically conducted corresponding to NA2, it is not necessary thatthe aperture limit element corresponding to the numerical aperture NA2of DVD is provided separately, in the third optical pickup device PU3.

On the one hand, because the objective optical system OBJ is notprovided with the aperture switching function to the wavelength λ3, itis necessary that the aperture limit element corresponding to thenumerical aperture NA3 of CD, is provided separately, and in theobjective optical system OBJ, as such an aperture limit element, awavelength selection filter WF is formed on the optical function surfaceS1 on the semiconductor laser light source side of the aberrationcorrecting element L1.

The wavelength selection filter WF has, as shown in FIG. 12, thewavelength selectivity of the transmission factor in which all ofwavelengths of λ1 to λ3 are passed in an area in NA3, and in an area ofthe outside of NA3, only the wavelength λ3 is cut off, and by such awavelength selectivity, the aperture switching corresponding to NA3 isconducted.

Hereupon, to the wavelength selection filter WF, the wavelengthselectivity of transmission factor as shown in FIG. 13, may also begiven. Because this wavelength selection filter WF has the wavelengthselectivity of the transmission factor in which all of wavelengths of λ1to λ3 are passed in an area in NA3, in an area from NA3 to NA2, only thewavelength λ3 is cut off, and in an area from NA2 to NA1, thewavelengths λ2 and λ3 are cut off, by such a wavelength selectivity, theaperture switching corresponding to NA2 and NA3 can be conducted.

Further, in the present embodiment, the wavelength selection filter WFis formed on the optical function surface of the aberration correctingelement L1, however, it may also be formed on the optical functionsurface of the light converging element L2, or an aperture limit elementAP in which such a wavelength selection filter WF is formed on itsoptical function surface, may be mounted separately. In this case, it ispreferable that the aperture limit element AP and the objective opticalsystem OBJ are integrally tracking-driven.

The Fourth Embodiment

FIG. 5 is a view generally showing a structure of the fourth opticalpickup device PU4 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.6 mm, numerical aperture NA1=0.65, the optical specificationof DVD is the wavelength λ2=658 nm, the thickness t2 of the protectivelayer PL2=0.6 mm, numerical aperture NA2=0.65, and the opticalspecification of CD is the wavelength λ3=785 nm, the thickness t3 of theprotective layer PL3=1.2 mm, numerical aperture NA3=0.50. However, acombination of the wavelength, thickness of the protective layer, andnumerical aperture is not limited to this.

The optical pickup device PU4 is structured by: a laser module LM1 forDVD/CD structured by the module MD1 for high density optical disk HD inwhich the blue violet semiconductor laser LD1 which is made to emitlight when the recording/reproducing of the information is conducted forthe high density optical disk HD and which projects the laser light fluxof 408 nm, and the light detector PD1 are integrated, the first lightemitting point EP1 which is made to emit light when therecording/reproducing of the information is conducted for DVD, and whichprojects the laser light flux of 658 nm, the second light emitting pointEP2 which is made to emit light when the recording/reproducing of theinformation is conducted for CD, and which projects the laser light fluxof 785 nm, the first light receiving section DS1 which light-receivesthe reflected light flux from the information recording surface RL2 ofDVD, the second light receiving section DS2 which light-receives thereflected light flux from the information recording surface RL3 of CD,and a prism PS; the objective optical system OBJ; 2-axis actuator AC;stop STO corresponding to numerical aperture NA 0.65 of the high densityoptical disk HD; polarized beam splitter BS; and collimator lens COL.

Hereupon, as the light source for the high density optical disk HD,other than the above-described blue violet semiconductor laser LD1, ablue violet SHG laser can also be used.

In the optical pickup device PU4, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 7, the module MD1 forthe high density optical disk HD, is actuated and the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is made almostparallel light flux via the collimator lens COL, and after transmits thepolarized beam splitter BS, the light flux diameter is regulated by stopSTO, and it becomes a spot formed on the information recording surfaceRL1 through the protective layer PL1 of the high density optical disk HDby the objective optical system OBJ. The objective optical system OBJconducts the focusing and tracking by 2-axis actuator AC arranged in itsperiphery. The reflected light flux modulated by the information pit onthe information recording surface RL1 is, after it transmits again theobjective optical system OBJ, stop STO, polarized beam splitter BS andcollimator lens COL, it becomes the converged light flux, and isconverged on the light receiving surface of the light detector PD1 ofthe module MD1 for the high density optical disk HD. Then, by using theoutput signal of the light detector PD1, the information recorded in thehigh density optical disk HD can be read.

Further, in the optical pickup device PU4, when therecording/reproducing of the information is conducted for DVD, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1 is, as the ray oflight path is drawn by a wave line in FIG. 7, reflected by the prism PS,and after reflected by the polarized beam splitter BS, it becomes a spotformed on the information recording surface RL2 through the protectivelayer PL2 of the DVD by the objective optical system OBJ. The objectiveoptical system OBJ conducts the focusing and tracking by 2-axis actuatorAC arranged in its periphery. The reflected light flux modulated by theinformation pit on the information recording surface RL2 transmits againthe objective optical system OBJ, and after reflected by the polarizedbeam splitter BS, it is reflected two times inside the prism PS, andlight converged in the light receiving section DS1. Then, by using theoutput signal of the light receiving section DS1, the informationrecorded in DVD can be read.

Further, in the optical pickup device PU4, when therecording/reproducing of the information is conducted for CD, the secondlight emitting point EP2 is made to emit light. The divergent light fluxprojected from the second light emitting point EP2 is, as the ray oflight path is drawn by a two dot chain line in FIG. 7, reflected by theprism PS, and after reflected by the polarized beam splitter BS, itbecomes a spot formed on the information recording surface RL1 throughthe protective layer PL1 of CD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL1 transmits again the objective optical system OBJ, and afterreflected by the polarized beam splitter BS, it is reflected two timesinside the prism PS, and light converged in the light receiving sectionDS2. Then, by using the output signal of the light receiving sectionDS2, the information recorded in CD can be read.

Next, a structure of the objective optical system OBJ will be described.The objective optical system OBJ is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, the refractive index to λ2 is1.5064, and the refractive index to λ3 is 1.5050.

The optical function surface S1 on the semiconductor laser light sourceside of the objective optical system OBJ is, as shown in FIG. 8, dividedinto the sixteenth optical function area AREA 16 including the opticalaxis corresponding to an area in the numerical aperture 0.50 of CD, andthe seventeenth optical function area AREA 17 corresponding to an areafrom the numerical aperture 0.50 of CD to the numerical aperture 0.65 ofthe high density optical disk HD (DVD), and in the sixteenth opticalfunction area AREA 16, the superposition type diffractive structuresHOE7, which is a structure in which a plurality of ring-shaped zonesinside of which the step structure is formed, are arranged around theoptical axis, is formed.

The width Λ7 of each ring-shaped zone of the superposition typediffractive structure HOE7, and the inclination direction of eachring-shaped zone are set so that, when the laser light flux ofwavelength λ2 enters into the superposition type diffractive structureHOE7, the spherical aberration amount of the over correction directionadded to +1-degree diffracted light ray by the diffraction action, andthe spherical aberration of under correction direction generated due toa case where the magnification m2 to wavelength λ2 and the magnificationm3 to wavelength λ3 are made almost the same, are cancelled each other.Hereby, the laser light flux of wavelength λ2 which transmits thesuperposition type diffractive structure HOE1 and the protective layerPL2 of DVD, forms a good spot on the information recording surface RL2of DVD.

Because a specific structure of the superposition type diffractivestructure HOE7 is the same as the structure of the superposition typediffractive structure HOE1 of the optical pickup device PU1, thedetailed description will be neglected herein.

Hereupon, also in the superposition type diffractive structure HOE7, inthe same manner as in the superposition type diffractive structure HOE1of the optical pickup device PU1, a structure in which it is set so thatthe paraxial diffraction power is positive, and when the laser lightflux of wavelength λ2 enters, the divergent degree of the laser lightflux of λ2 is made small, and projected, may also be applied.

Further, on the entire surface of the optical function surface S1 on thesemiconductor laser light source side of the objective optical systemOBJ, an optical pass difference grant structure NPS which is a structurefor suppressing the spherical aberration change following thetemperature change of the objective optical system OBJ in the blueviolet area, is formed.

In the optical path difference grant structure NPS, the height d11 ofthe stepped section closest to the optical axis is designed so that theoptical path difference of 10×λ1 (μm) is added to the wavelength λ1between adjoining step structures.

By adjoining ring-shaped zones divided by this stepped section, when theoptical path differences Φ2 and Φ3 added to each wavelength ofwavelengths λ2 and λ3 are calculated, Φ2=5.99, Φ3=5.01. Because Φ2 andΦ3 are about integers, the generation of the high-degree of sphericalaberration by the optical path difference grant structure NPS is small,and the high transmission factor can be realized.

Further, as shown in FIG. 8, in the optical path difference grantstructure NPS, the ring-shaped zone adjoining the outside of the centralarea is formed by shifting in the optical axis direction so that theoptical path length is shortened to the central area, and thering-shaped zone in the maximum effective diameter position is formed byshifting in the optical axis direction so that the optical path lengthis lengthened to the ring-shaped zone adjoining its inside, and thering-shaped zone in the position of 75% of the maximum effectivediameter is formed by shifting in the optical axis direction so that theoptical path length is shortened to the ring-shaped zone adjoining itsinside, and to the ring-shaped zone adjoining its outside.

Because the optical path difference grant structure NPS of such astructure has a refractive index dependency of the spherical aberrationin which the spherical aberration changes to under correction directionwhen the refractive index is lowered, and the spherical aberrationchanges to over correction direction when the refractive index isheightened, the spherical aberration change following the temperaturechange of the objective optical system OBJ in the blue violet area canbe suppressed.

Hereupon, on the entire surface of the optical function surface on theoptical disk side of the collimator lens COL, the diffractive structureDOE7 structured by a plurality of ring-shaped zones whose sectionalshape including the optical axis is a saw-toothed shape, is formed, andthis is a structure for suppressing the chromatic aberration of theobjective optical system OBJ in the blue violet area.

Herein, an aperture switching when the recording/reproducing of theinformation is conducted for CD, in the fourth optical pickup device PU4of the present embodiment, will be described.

In the fourth optical pickup device PU4, because NA1 (=NA2) and NA3 aredifferent, when the recording/reproducing of the information isconducted for CD, it is necessary that the aperture is switchedcorresponding to the numerical aperture NA3.

Because the objective optical system OBJ is not provided with theaperture switching function to the wavelength λ3, it is necessary thatthe aperture limit element corresponding to the numerical aperture NA3of CD, is provided separately, and in the objective optical system OBJ,as such an aperture limit element, a wavelength selection filter WF isformed on the optical function surface S1 on the semiconductor laserlight source side.

The wavelength selection filter WF has, as shown in FIG. 12, thewavelength selectivity of the transmission factor in which all ofwavelengths of λ1 to λ3 are passed in an area in NA3, and in an area ofthe outside of NA3, only the wavelength λ3 is cut off, and by such awavelength selectivity, the aperture switching corresponding to NA3 isconducted.

Further, when NA1, NA2 and NA3 are different each other, it ispreferable that, to the wavelength selection filter WF, the wavelengthselectivity of transmission factor as shown in FIG. 13 is given. Becausethis wavelength selection filter WF has the wavelength selectivity ofthe transmission factor in which all of wavelengths of λ1 to λ3 arepassed in an area in NA3, in an area from NA3 to NA2, only thewavelength λ3 is cut off, and in an area from NA2 to NA1, thewavelengths λ2 and λ3 are cut off, by such a wavelength selectivity, theaperture switching corresponding to NA2 and NA3 can be conducted.

Further, in the present embodiment, the wavelength selection filter WFis formed on the optical function surface of the objective opticalsystem OBJ, however, an aperture limit element AP in which such awavelength selection filter WF is formed on its optical functionsurface, may be mounted separately. In this case, it is preferable thatthe aperture limit element AP and the objective optical system OBJ areintegrally tracking-driven by the two-axis actuator AC.

The Fifth Embodiment

FIG. 14 is a view generally showing a structure of the fifth opticalpickup device PU5 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.60, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU5 is structured by: a module MD1 for highdensity optical disk HD in which the blue violet semiconductor laser LD1which is made to emit light when the recording/reproducing of theinformation is conducted for the high density optical disk HD and whichprojects the laser light flux of 408 nm, and the light detector PD1 areintegrated; the module MD2 for DVD in which the red semiconductor laserLD2 which is made to emit light when the recording/reproducing of theinformation is conducted for DVD and which projects the laser light fluxof 658 nm, and the light detector PD2 are integrated; and module MD3 forCD in which the infrared semiconductor laser LD3 which is made to emitlight when the recording/reproducing of the information is conducted forCD and which projects the laser light flux of 785 nm, and the lightdetector PD3 are integrated; the objective optical system OBJ structuredby the aberration correcting element L1 and the light converging elementL2 which has a function by which the laser light fluxes transmitted thisaberration correcting element L1 are light converged on the informationrecording surfaces RL1, RL2, RL3, and whose both surfaces are asphericalsurfaces; aperture limit element AP; 2-axis actuator AC; stop STOcorresponding to numerical aperture NA 0.85 of the high density opticaldisk HD; first polarized beam splitter BS1; second polarized beamsplitter BS2; collimator lens COL; 1-axis actuator UAC; and beam shapingelement SH.

In the optical pickup device PU5, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 14, the module MD1for the high density optical disk HD is actuated and the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is, when ittransmits the beam shaping element SH, its sectional shape is shapedfrom elliptical to circular, and it transmits the first polarized beamsplitter BS1, and after it is made almost parallel light flux by thecollimator lens COL, it transmits the second polarized beam splitterBS2, and the light flux diameter is regulated by stop STO, it transmitsthe aperture limit element AP, and it becomes a spot formed on theinformation recording surface RL1 through the protective layer PL1 ofthe high density optical disk HD by the objective optical system OBJ.The objective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL1, after it transmits again the objective optical system OBJ, aperturelimit element AP, second polarized beam splitter BS2 and collimator lensCOL, becomes the converged light flux, and transmits the first polarizedbeam splitter BS1 and beam shaping element SH, and is converged on thelight receiving surface of the light detector PD1 of the module MD1 forthe high density optical disk HD. Then, by using the output signal ofthe light detector PD1, the information recorded in the high densityoptical disk HD can be read.

Further, in the optical pickup device PU5, when therecording/reproducing of the information is conducted for DVD, as itsray of light path is drawn by a dotted line in FIG. 14, the module MD2for DVD is actuated and the red semiconductor laser LD2 is made to emitlight. The divergent light flux projected from the red semiconductorlaser LD2 is reflected by the first polarized beam splitter BS1, andafter it is converted into parallel light flux by the collimator lensCOL, it transmits the second polarized beam splitter BS2, the light fluxdiameter is regulated by the aperture limit element AP, it becomes aspot formed on the information recording surface RL2 through theprotective layer PL2 of DVD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL2, after it transmits again the objective optical system OBJ, aperturelimit element AP, second polarized beam splitter BS2 and collimator lensCOL, becomes the converged light flux, and it is reflected by the firstpolarized beam splitter BS1, and converged on the light receivingsurface of the light detector PD2 of the module MD2 for DVD. Then, byusing the output signal of the light detector PD2, the informationrecorded in DVD can be read.

Further, when the recording/reproducing of the information is conductedfor CD, as its ray of light path is drawn by a two dot chain line inFIG. 14, the module MD3 for CD is actuated and the infraredsemiconductor laser LD3 is made to emit light. In the divergent lightflux projected from the infrared semiconductor laser LD3, after it isreflected by the second polarized beam splitter BS2, the light fluxdiameter is regulated by the aperture limit element AP, it becomes aspot formed on the information recording surface RL3 through theprotective layer PL3 of CD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL3, after it transmits again the objective optical system OBJ, it isreflected by the second polarized beam splitter BS2, and converged onthe light receiving surface of the light detector PD3 of the module MD3for CD. Then, by using the output signal of the light detector PD3, theinformation recorded in CD can be read.

Next, a structure of the objective optical system OBJ will be described.The aberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, the refractive index to λ2 is1.5064, and the refractive index to λ3 is 1.5050. Further, the lightconverging element L2 is a plastic lens, in which the refractive indexnd on d-line is 1.5435, and Abbe's number νd is 56.3. Further, in theperiphery of respective optical function sections (areas of theaberration correcting element L1 and light converging element L2 throughwhich the laser light flux from the blue violet semiconductor laser LD1passes), flange sections FL1, FL2 integrally molded with the opticalfunction section are provided, and when both of a part of such flangesections FL1, FL2 are mutually connected together, they are integrated.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, as shown in FIG. 15(a), divided into the eighteenth optical function area AREA 18 includingthe optical axis corresponding to an area in the numerical aperture 0.60of DVD, and the nineteenth optical function area AREA 19 correspondingto an area from the numerical aperture 0.60 of DVD to the numericalaperture 0.85 of the high density optical disk, and in the eighteenthoptical function area AREA 18, the superposition type diffractivestructure HOE8, which is a structure in which a plurality of ring-shapedzones inside of which the step structure is formed, are arranged aroundthe optical axis, is formed.

Because a structure of the superposition type diffractive structure HOE8formed in the eighteenth optical function area AREA 18 is the same asthe superposition type diffractive structure HOE4 in the second opticalpickup device PU2, the detailed description is omitted here.

Further, the optical function surface S2 on the optical disk side of theaberration correcting element L1 is, as shown in FIG. 15( c), dividedinto the twentieth optical function area AREA 20 including the opticalaxis corresponding to an area in numerical aperture 0.60 of DVD, and thetwenty-first optical function area AREA 21 corresponding to an area fromthe numerical aperture 0.60 of DVD to the numerical aperture 0.85 of thehigh density optical disk HD, and the diffractive structures DOE8, DOE9structured by a plurality of ring-shaped zones including the opticalaxis, whose sectional shape is the saw-toothed shape, are respectivelyformed in the optical function area AREA 20 and the optical functionarea AREA 21.

The diffractive structures DOE8, DOE9 are structures for suppressing thechromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration change following thetemperature change, and because the structures of them are the same asdiffractive structures DOE3, DOE4 in the optical pickup device PU2, thedetailed description is omitted herein.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, and diffractive structure is formed on the opticalfunction surface S2 on the optical disk side, is applied, in contrast tothis, a structure in which the diffractive structure is formed on theoptical function surface S1 on the semiconductor laser light sourceside, and the superposition type diffractive structure is formed on theoptical function surface S2 on the optical disk side, may also beapplied.

Further, the collimator lens COL of the present embodiment is structuredso that the position can be shifted in the optical axis direction by the1-axis actuator UAC. Hereby, because the spherical aberration of a spotformed on the information recording surface RL1 of the high densityoptical disk HD can be corrected, a good recording/reproducingcharacteristic can be always maintained for the high density opticaldisk HD.

Causes of generation of the spherical aberration corrected by theposition adjustment of the collimator lens COL are, for example, awavelength dispersion by the production error of the blue violetsemiconductor laser LD1, the refractive index change or refractive indexdistribution of the objective optical system OBJ following thetemperature change, a focus-jump between layers at the time ofrecording/reproducing for the multi-layer disk such as 2-layer disk,4-layer disk, and the thickness dispersion or thickness distribution bythe production error of the protective layer PL1.

In above description, a case where the spherical aberration of a spotformed on the information recording surface RL1 of the high densityoptical disk HD is corrected, is described, however, it may also beallowable that the spherical aberration of a spot formed on theinformation recording surface RL2 of DVD, is corrected by the positionadjustment of the collimator lens COL.

Further, in the present embodiment, when the recording/reproducing ofthe information is conducted for DVD or CD, as an element for switchingthe aperture of the objective optical system OBJ, corresponding to thenumerical aperture NA of respective optical disks, an aperture limitelement AP which is integrated with the objective optical system OBJthrough a connection member B, is provided.

On the optical function surface of the aperture limit element AP, thewavelength selection filter WF having the wavelength selectivity of thetransmission factor as shown in FIG. 13, is formed. Because thiswavelength selection filter WF has the wavelength selectivity of thetransmission factor in which all of wavelengths of λ1 to λ3 are passedin an area in NA3, and in an area from NA3 to NA2, only the wavelengthλ3 is cut off, and in an area from NA2 to NA1, wavelengths λ2 and λ3 arecut off, by such a wavelength selectivity, the aperture switchingcorresponding to NA3 is conducted.

Hereupon, to the wavelength selection filter WF, the wavelengthselectivity of transmission factor as shown in FIG. 13, may also begiven. Because this wavelength selection filter WF has the wavelengthselectivity of the transmission factor in which all of wavelengths of λ1to λ3 are passed in an area in NA3, in an area from NA3 to NA2, only thewavelength λ3 is cut off, and in an area from NA2 to NA1, thewavelengths λ2 and λ3 are cut off, by such a wavelength selectivity, theaperture switching corresponding to NA2 and NA3 can be conducted.

Hereupon, because the objective optical system OBJ in the presentembodiment has, in the same manner as the second optical pickup devicePU2 and the third optical pickup device PU3, the aperture switchingfunction corresponding to the numerical aperture NA2 of DVD, to thewavelength selection filter WF, the wavelength selectivity oftransmission factor as shown in FIG. 12 may also be given.

The Sixth Embodiment

FIG. 18 is a view generally showing a structure of the sixth opticalpickup device PU6 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.60, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU6 is structured by: a module MD1 for highdensity optical disk HD in which the blue violet semiconductor laser LD1which is made to emit light when the recording/reproducing of theinformation is conducted for the high density optical disk HD and whichprojects the laser light flux of 408 nm, and the light detector PD1 areintegrated; laser module LM1 for DVD/CD structured: by the first lightemitting point EP1 which is made to emit light when therecording/reproducing of the information is conducted for DVD and whichprojects the laser light flux of 658 nm; the second light emitting pointEP2 which is made to emit light when the recording/reproducing of theinformation is conducted for CD and which projects the laser light fluxof 785 nm; the first light receiving section DS1 which light receivesthe reflected light flux from the information recording surface RL2 ofDVD; and the second light receiving section DS2 which light receives thereflected light flux from the information recording surface RL3 of CD;and prism PS; the objective optical system OBJ structured by theaberration correcting element L1 and the light converging element L2which has a function by which the laser light fluxes transmitted thisaberration correcting element L1 are light converged on the informationrecording surfaces RL1, RL2, RL3, LD3, and both surfaces of which areaspherical surfaces; an aperture limit element AP; 2-axis actuator AC;stop STO corresponding to the numerical aperture NA 0.85 of the highdensity optical disk HD; 1-axis actuator UAC; expander lens EXP;polarized beam splitter BS; collimator lens COL; coupling CUL; and beamshaping element SH.

Hereupon, as the light source for the high density optical disk HD,other than the above blue violet semiconductor laser LD1, a blue violetSHG laser can also be used.

The expander lens EXP is structured by the first lens EXP1 whoseparaxial refractive power is negative, and the second lens EXP2 whoseparaxial refractive power is positive.

In the optical pickup device PU6, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 18, the module MD1for the high density optical disk HD is actuated and the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is, when ittransmits the beam shaping element SH, after its sectional shape isshaped from elliptical to circular, it is converted into parallel lightflux by the collimator lens COL, and when it transmits the first lensEXPL, second lens EXP2, its diameter is enlarged, and after it transmitsthe polarized beam splitter BS, the light flux diameter is regulated bythe stop STO, and it transmits the aperture limit element AP, and itbecomes a spot formed on the information recording surface RL1 throughthe protective layer PL1 of the high density optical disk HD by theobjective optical system OBJ. The objective optical system OBJ conductsthe focusing and tracking by 2-axis actuator AC arranged in itsperiphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL1, after it transmits again theobjective optical system OBJ, aperture limit element AP, polarized beamsplitter BS, second lens EXP2, first lens EXP1, expander lens EXP andcollimator lens COL, becomes the converged light flux and transmits thebeam shaping element SH, and is converged on the light receiving surfaceof the light detector PD1 of the module MD1 for the high density opticaldisk HD. Then, by using the output signal of the light detector PD1, theinformation recorded in the high density optical disk HD can be read.

Further, in the optical pickup device PU6, when therecording/reproducing of the information is conducted for DVD, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1 is, as the ray oflight path is drawn by a wave line in FIG. 18, reflected by the prismPS, and after it is converted into the parallel light flux by thecoupling lens CUL, it is reflected by the polarized beam splitter BS,and it becomes a spot formed on the information recording surface RL2through the protective layer PL2 of DVD by the objective optical systemOBJ. The objective optical system OBJ conducts the focusing and trackingby 2-axis actuator AC arranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL2, after it transmits again theobjective optical system OBJ, it becomes the converged light flux by thecoupling lens CUL, and is reflected 2 times inside the prism PS, andlight converged on the light receiving section DS1. Then, by using theoutput signal of the light detector DS1, the information recorded in DVDcan be read.

Further, in the optical pickup device PU6, when therecording/reproducing of the information is conducted for DVD, the firstlight emitting point EP1 is made to emit light. The divergent light fluxprojected from the first light emitting point EP1 is, as the ray oflight path is drawn by a wave line in FIG. 18, reflected by the prismPS, and after it is converted into the parallel light flux by thecoupling lens CUL, it is reflected by the polarized beam splitter BS,and it becomes a spot formed on the information recording surface RL2through the protective layer PL2 of DVD by the objective optical systemOBJ. The objective optical system OBJ conducts the focusing and trackingby 2-axis actuator AC arranged in its periphery.

Further, in the optical pickup device PU6, when therecording/reproducing of the information is conducted for CD, the firstlight emitting point EP2 is made to emit light. The divergent light fluxprojected from the first light emitting point EP2 is, as the ray oflight path is drawn by a two dot chain line in FIG. 18, after reflectedby the prism PS, and the divergent angle is converted by the couplinglens CUL, and after reflected by the polarized beam splitter BS, thelight flux diameter is regulated by the aperture limit element AP, andit becomes a spot formed on the information recording surface RL1through the protective layer PL1 of CD by the objective optical systemOBJ. The objective optical system OBJ conducts the focusing and trackingby 2-axis actuator AC arranged in its periphery. The reflected lightflux modulated by the information pit on the information recordingsurface RL1, after it transmits again the objective optical system OBJand aperture limit element AP, and reflected by the polarized beamsplitter BS, and it is reflected two times inside the prism PS, andlight converged on the light receiving section DS2. Then, by using theoutput signal of the light receiving section DS2, the informationrecorded in CD can be read.

Next, a structure of the objective optical system OBJ will be described.The aberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, the refractive index to λ2 is1.5064, and the refractive index to λ3 is 1.5050. Further, the lightconverging element L2 is a glass lens, in which the refractive index ndon d-line is 1.6062, and Abbe's number νd is 61.2. Further, theaberration correcting element L1, light converging element L2 andaperture limit element AP are integrated through a connection member B.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, although graphicdisplay is neglected, divided into the 22-th optical function area AREA22 including the optical axis corresponding to an area in the numericalaperture 0.60 of DVD, and the 23-th optical function area AREA 23corresponding to an area from the numerical aperture 0.60 of DVD to thenumerical aperture 0.85 of the high density optical disk HD, and in the22-th optical function area AREA 22, the superposition type diffractivestructure HOE9, which is a structure in which a plurality of ring-shapedzones inside of which the step structure is formed, are arranged aroundthe optical axis, is formed.

Because the structure of the superposition type diffractive structureHOE9 formed in the 22-th optical function area AREA 22 is the same asthe superposition type diffractive structure HOE4 in the second opticalpickup device PU2, the detailed description will be omitted herein.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, is applied, in contrast to this, a structure in whichthe superposition type diffractive structure is formed on the opticalfunction surface S2 on the optical disk side, may also be applied.

Further, the first lens EXP1 of the expander lens EXP of the presentembodiment is structured so that the position can be shifted in theoptical axis direction by the 1-axis actuator UAC. Hereby, because thespherical aberration of a spot formed on the information recordingsurface RL1 of the high density optical disk HD can be corrected, a goodrecording/reproducing characteristic can be always maintained for thehigh density optical disk HD.

Causes of generation of the spherical aberration corrected by theposition adjustment of the first lens EXPL are, for example, awavelength dispersion by the production error of the blue violetsemiconductor laser LD1, the refractive index change or refractive indexdistribution of the objective optical system OBJ following thetemperature change, a focus-jump between layers at the time ofrecording/reproducing for the multi-layer disk such as 2-layer disk,4-layer disk, and the thickness dispersion or thickness distribution bythe production error of the protective layer PL1.

Further, on the optical function surface on the optical disk side of thesecond lens EXP2, the diffractive structure DOE10 structured by aplurality of ring-shaped zones whose sectional shape is a saw-toothedshape, is formed. The diffractive structure DOE10 is a structure forcorrecting the chromatic aberration of the objective optical system OBJin the blue violet area, and the paraxial diffraction power of thediffractive structure DOE10 is determined so that the paraxial power Pλ1of the second lens EXP2 to the wavelength λ1, the paraxial power Pλ1+10of the second lens EXP2 to the wavelength λ1+10 (nm), and the paraxialpower Pλ1−10 of the second lens EXP2 to the wavelength λ1+10 (nm),satisfy the following relationship:

Pλ1+10<Pλ1<Pλ1−10.

Further, the coupling lens CUL is an optical element by which thedivergent angles of the laser light flux of the wavelength λ2 projectedfrom the first light emitting point EP1 and the laser light flux of thewavelength λ3 projected from the second light emitting point EP2 arerespectively converted into the divergent angles corresponding to themagnification m2 to the wavelength λ2 of the objective optical systemOBJ, and the magnification m3 to the wavelength λ3, and they areprojected. In the present embodiment, because m2=0, when the laser lightflux of the wavelength λ2 projected from the first light emitting pointEP1 transmits the coupling lens CUL, it is converted into a parallellight flux.

The coupling lens CUL is a plastic lens in which the refractive index ndon d-line is 1.5091, and Abbe's number νd is 56.5, and the refractiveindex to λ2 is 1.5064, and the refractive index to λ3 is 1.5050.

The optical function surface on the optical disk side of the couplinglens CUL is, although graphic display is neglected, divided into the24-th optical function area AREA 24 including the optical axiscorresponding to an area in numerical aperture 0.45 of CD, and the 25-thoptical function area AREA 25 corresponding to an area from numeralaperture 0.45 of CD to numeral aperture 0.60 of DVD, and thesuperposition type diffractive structure HOE10 which is a structure inwhich a plurality of ring-shaped zones inside of which step structure isformed, are arranged around the optical axis, is formed in the 24-thoptical function area AREA 24.

Because the structure of the superposition type diffractive structureHOE10 formed in the 24-th optical function area AREA 24 is the same asthe superposition type diffractive structure HOE6 in the third opticalpickup device PU3, the detailed description will be omitted herein.

Further, in the present embodiment, when the recording/reproducing ofthe information is conducted for CD, as an element for switching theaperture of the objective optical system OBJ corresponding to thenumerical aperture NA3 of CD, an aperture limit element AP integratedwith the objective optical system OBJ through the connection member B isprovided.

A wavelength selection filter WF having the wavelength selectivity ofthe transmission factor as shown in FIG. 12 is formed on the opticalfunction surface of the aperture limit element AP. This wavelengthselection filter WF has the wavelength selectivity of the transmissionfactor in which all of wavelengths of λ1 to λ3 are passed in an area inNA3, and in an area of the outside of NA3, only the wavelength λ3 is cutoff, and by such a wavelength selectivity, the aperture switchingcorresponding to NA3 is conducted.

Hereupon, the objective optical system OBJ in the present embodiment hasthe aperture switching function corresponding to the numerical apertureNA2 of DVD in the same as the second optical pickup device PU2, thirdoptical pickup device PU3, and fifth optical pickup device PU5, and bythis aperture switching function, the aperture switching correspondingto NA2 is conducted.

The Seventh Embodiment

FIG. 19 is a view generally showing a structure of the seventh opticalpickup device PU7 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk HD is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.60, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU7 is structured by: a module MD3 for CD inwhich the blue violet semiconductor laser LD1 which is made to emitlight when the recording/reproducing of the information is conducted forthe high density optical disk HD and which projects the laser light fluxof 408 nm; red semiconductor laser LD2 which is made to emit light whenthe recording/reproducing of the information is conducted for DVD andwhich projects the laser light flux of 658 nm; light detector PD1 whichis commonly used for the high density optical disk HD and DVD; themodule MD3 for CD in which the infrared semiconductor laser LD3 which ismade to emit light when the recording/reproducing of the information isconducted for CD and which projects the laser light flux of 785 nm, andthe light detector PD3 are integrated; objective optical system OBJstructured by the aberration correcting element L1 and the lightconverging element L2 which has a function by which the laser lightfluxes transmitted this aberration correcting element LI are lightconverged on the information recording surfaces RL1, RL2, RL3, LD3, andboth surfaces of which are aspherical surfaces; wavelength selectionfilter WF; liquid crystal phase control element LCD; 2-axis actuator AC;stop STO corresponding to the numerical aperture NA 0.85 of the highdensity optical disk HD; first polarized beam splitter BS1; secondpolarized beam splitter BS2; third polarized beam splitter BS3; firstcollimator lens COL1; second collimator lens Col2; sensor lens SEN; andbeam shaping lens BS.

Hereupon, as the light source for the high density optical disk HD,other than the above blue violet semiconductor laser LD1, a blue violetSHG laser can also be used.

In the optical pickup device PU7, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 19, the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is, whentransmits the beam shaping element SH, after its sectional shape isshaped from elliptical to circular, converted to parallel light flux bythe first collimator lens COL, and after it transmits the first to thirdpolarized beam splitters BS1, BS2, BS3, the light flux diameter isregulated by stop STO, and transmits the wavelength selection filter WF,liquid crystal phase control element LCD, and it, becomes a spot formedon the information recording surface RL1 through the protective layerPL1 of the high density optical disk HD by the objective optical systemOBJ. The objective optical system OBJ conducts the focusing and trackingby 2-axis actuator AC, arranged in its periphery. The reflected lightflux modulated by the information pit on the information recordingsurface RL1 is, after it transmits again the objective optical systemOBJ, liquid crystal phase control element LCD, wavelength selectionfilter WF, third polarized beam splitter BS3, reflected by the secondpolarized beam splitter BS2, and the astigmatism is given by the sensorlens SEN and it is converted into the converged light flux, andconverged on the light receiving surface of the light detector PD1.Then, by using the output signal of the light detector PD1, theinformation recorded in the high density optical disk HD can be read.

Further, in the optical pickup device PU7, when therecording/reproducing of the information is conducted for DVD, as itsray of light path is drawn by a dotted line in FIG. 19, the redsemiconductor laser LD2 is made to emit light. The divergent light fluxprojected from the red semiconductor laser LD2 is converted intoparallel light flux by the second collimator lens COL2, and after it isreflected by the first polarized beam splitters BS1, it transmits thesecond and third polarized beam splitters BS2, BS3, and transmits thewavelength selection filter WF, liquid crystal phase control elementLCD, and it becomes a spot formed on the information recording surfaceRL2 through the protective layer PL2 of DVD by the objective opticalsystem OBJ. The objective optical system OBJ conducts the focusing andtracking by 2-axis actuator AC arranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL2 is, after it transmits again theobjective optical system OBJ, liquid crystal phase control element LCD,wavelength selection filter WF, third polarized beam splitter BS3,reflected by the second polarized beam splitter BS2, and the astigmatismis given by the sensor lens SEN and it is converted into the convergedlight flux, and converged on the light receiving surface of the lightdetector PD1. Then, by using the output signal of the light detectorPD1, the information recorded in DVD can be read.

Further, when the recording/reproducing of the information is conductedfor CD, as its ray of light path is drawn by a two-dot chain line inFIG. 19, the module MD3 for CD is actuated, and the infraredsemiconductor laser LD3 is made to emit light. The divergent light fluxprojected from the infrared semiconductor laser LD3, after it isreflected by the third polarized beam splitter BS3, the light fluxdiameter is regulated by the wavelength selection filter WF, ittransmits the liquid crystal phase control element LCD, and it becomes aspot formed on the information recording surface RL3 through theprotective layer PL3 of CD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL3 is, after it transmits again theobjective optical system OBJ, liquid crystal phase control element LCD,wavelength selection filter WF, reflected by the third polarized beamsplitter BS3, and converged on the light receiving surface of the lightdetector PD3 of the module MD3 for CD. Then, by using the output signalof the light detector PD3, the information recorded in CD can be read.

Next, a structure of the objective optical system OBJ will be described.The aberration correcting element L1 is a plastic lens, in which therefractive index nd on d-line is 1.5091, and Abbe's number νd is 56.5,and the refractive index to λ1 is 1.5242, the refractive index to λ2 is1.5064, and the refractive index to λ3 is 1.5050. Further, the lightconverging element L2 is a plastic lens, in which the refractive indexnd on d-line is 1.5435, and Abbe's number νd is 56.3. Further, in theperiphery of respective optical function section (an area of theaberration correcting element L1, and light converging element L2through the laser light flux from the blue violet semiconductor laserLD1 passes), flange sections FL1, FL2 which are integrally molded withthe optical function section, are provided, and they are integrated bymutually connecting both of a part of such flange sections FL1 and FL2.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, although graphicdisplay is neglected, divided into the 26-th optical function area AREA26 including the optical axis corresponding to an area in the numericalaperture 0.60 of DVD, and the 27-th optical function area AREA 27corresponding to an area from the numerical aperture 0.60 of DVD to thenumerical aperture 0.85 of the high density optical disk HD, and in the26-th optical function area AREA 26, the superposition type diffractivestructure HOE11, which is a structure in which a plurality ofring-shaped zones inside of which the step structure is formed, arearranged around the optical axis, is formed.

Because the structure of the superposition type diffractive structureHOE11 formed in the 26-th optical function area AREA 26 is the same asthe superposition type diffractive structure HOE4 in the second opticalpickup device PU2, the detailed description will be omitted herein.

Further, the optical function surface S2 on the optical disk side of theaberration correcting element L1 is, although graphic display isneglected, divided into the 28-th optical function area AREA 28including the optical axis corresponding to an area in the numericalaperture 0.60 of DVD, and the 29-th optical function area AREA 29corresponding to an area from the numerical aperture 0.60 of DVD to thenumerical aperture 0.85 of the high density optical disk HD, anddiffractive structures DOE11 and DOE12 structured by a plurality ofring-shaped zones whose sectional shape including the optical axis is asaw-toothed shape, are respectively formed in the 28-th optical functionarea AREA 28, and the 29-th optical function area AREA 29.

Diffractive structures DOE11 and DOE12 are structures for suppressingthe chromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration change following thetemperature change, and because the structure is the same as diffractivestructures DOE3 and DOE4 in the second optical pickup device PU2, thedetailed description will be omitted herein.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, and the type diffractive structure is formed on theoptical function surface S2, is applied, however, in contrast to this, astructure in which the type diffractive structure is formed on theoptical function surface S1 on the semiconductor laser light sourceside, and superposition type diffractive structure is formed on theoptical function surface S2 on the optical disk side, may also beapplied.

Further, the liquid crystal phase control element LCD is structured by aliquid crystal layer by which the phase change is generated to thetransmitting light flux by the impression of voltage, an electrode layeropposing each other to impress the voltage on the liquid crystalelement, and a power source to supply the voltage to the electrodelayer. At least one of the electrode layer opposing each other, isdivided into a predetermined pattern, and when the voltage is impressedon this electrode layer, the orientation condition of the liquid crystalelement is changed, and a predetermined phase can be added to thetransmitting light flux. Hereby, because the spherical aberration of aspot formed on the information recording surface RL1 of the high densityoptical disk HD can be corrected, a good recording/reproducingcharacteristic can be always maintained to the high density optical diskHD.

Causes of generation of the spherical aberration corrected by the liquidcrystal phase control element LCD are, for example, a wavelengthdispersion by the production error of the blue violet semiconductorlaser LD1, the refractive index change or refractive index distributionof the objective optical system OBJ following the temperature change, afocus-jump between layers at the time of recording/reproducing for themulti-layer disk such as 2-layer disk, 4-layer disk, and the thicknessdispersion or thickness distribution by the production error of theprotective layer PL1.

In the above description, a case where the spherical aberration of aspot formed on the information recording surface RL1 of the high densityoptical disk HD is corrected, is described, however, the sphericalaberration formed on the information recording surface RL2 of DVD, orthe spherical aberration formed on the information recording surface RL3of CD, may also be corrected by the liquid crystal phase control elementLCD. Particularly, when the recording/reproducing of the information isconducted for CD, by the liquid crystal phase control element LCD, bycorrecting the spherical aberration generated due to the differencebetween the protective layer PL1 and protective layer PL3, because themagnification m3 of the objective optical system OBJ to the third lightflux can be set larger, the generation of coma at the time of trackingdrive can be suppressed small.

Further, the objective optical system OBJ and the liquid crystal phasecontrol element LCD are integrated through a connection member B.

Further, in the present embodiment, when the recording/reproducing ofthe information is conducted for CD, corresponding to numerical apertureNA3 of CD, the wavelength selection filter WF to switch the aperture ofthe objective optical system OBJ is formed on the semiconductor laserlight source side of the liquid crystal phase control element LCD.

The wavelength selection filter WF has, as shown in FIG. 12, thewavelength selectivity of the transmission factor in which all ofwavelengths of λ1 to λ3 are passed in an area in NA3, and in an area ofthe outside of NA3, only the wavelength λ3 is cut off, and by such awavelength selectivity, the aperture switching corresponding to NA3 isconducted.

Hereupon, the objective optical system OBJ in the present embodimenthas, in the same manner as the second optical pickup device PU2, thethird optical pickup device PU3, the fifth optical pickup device PU5,the aperture switching function corresponding to the numerical apertureNA2 of DVD, and by this aperture switching function, the apertureswitching corresponding to NA2, is conducted.

The Eighth Embodiment

FIG. 19 is a view generally showing a structure of the seventh opticalpickup device PU7 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, DVD and CD. The optical specification of the high density opticaldisk HD is the wavelength λ1=408 nm, the thickness t1 of the protectivelayer PL1=0.875 mm, numerical aperture NA1=0.85, the opticalspecification of DVD is the wavelength λ2=658 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.60, and theoptical specification of CD is the wavelength λ3=785 nm, the thicknesst3 of the protective layer PL3=1.2 mm, numerical aperture NA3=0.45.However, a combination of the wavelength, thickness of the protectivelayer, and numerical aperture is not limited to this.

The optical pickup device PU8 is structured by: a blue violetsemiconductor laser LD1 which is made to emit light when therecording/reproducing of the information is conducted for the highdensity optical disk HD and which projects the laser light flux of 407nm; red semiconductor laser LD2 which is made to emit light when therecording/reproducing of the information is conducted for DVD and whichprojects the laser light flux of 660 nm; light detector PD which iscommonly used for the high density optical disk HD and DVD; objectiveoptical system OBJ structured by the aberration correcting element L1and the light converging element L2 which has a function by which thelaser light fluxes transmitted this aberration correcting element L1 arelight converged on the information recording surfaces RL1, RL2, and bothsurfaces of which are aspherical surfaces; liquid crystal phase controlelement LCD; 2-axis actuator AC; stop STO corresponding to the numericalaperture NA 0.85 of the high density optical disk HD; first polarizedbeam splitter BS1; second polarized beam splitter BS2, first collimatorlens COL1; second collimator lens Col2; sensor lens SEN; and beamshaping lens BS.

Hereupon, as the light source for the high density optical disk HD,other than the above blue violet semiconductor laser LD1, a blue violetSHG laser can also be used.

In the optical pickup device PU8, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 20, the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is, whentransmits the beam shaping element SH, after its sectional shape isshaped from elliptical to circular, converted to parallel light flux bythe first collimator lens COL, and after it transmits the first andsecond polarized beam splitters BS1, BS2, the light flux diameter isregulated by stop STO, and transmits the liquid crystal phase controlelement LCD, and it becomes a spot formed on the information recordingsurface RL1 through the protective layer PL1 of the high density opticaldisk HD by the objective optical system OBJ. The objective opticalsystem OBJ conducts the focusing and tracking by 2-axis actuator ACarranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL1 is, after it transmits again theobjective optical system OBJ, and liquid crystal phase control elementLCD, it is reflected by the second polarized beam splitter BS2, and theastigmatism is given by the sensor lens SEN and it is converted into theconverged light flux, and converged on the light receiving surface ofthe light detector PD1. Then, by using the output signal of the lightdetector PD1, the information recorded in the high density optical diskHD can be read.

Further, in the optical pickup device PU8, when therecording/reproducing of the information is conducted for DVD, as itsray of light path is drawn by a dotted line in FIG. 20, the redsemiconductor laser LD2 is made to emit light. The divergent light fluxprojected from the red semiconductor laser LD2 is converted intoparallel light flux by the second collimator lens COL2, and after it isreflected by the first polarized beam splitter BS1, it transmits thesecond polarized beam splitter BS2, and liquid crystal phase controlelement LCD, and it becomes a spot formed on the information recordingsurface RL2 through the protective layer PL2 of DVD by the objectiveoptical system OBJ. The objective optical system OBJ conducts thefocusing and tracking by 2-axis actuator AC arranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL2, after it transmits again theobjective optical system OBJ, and liquid crystal phase control elementLCD, it is reflected by the second polarized beam splitter BS2, and theastigmatism is given by the sensor lens SEN, and it is converted intothe converged light flux, and converged on the light receiving surfaceof the light detector PD1. Then, by using the output signal of the lightdetector PD1, the information recorded in DVD can be read.

Next, a structure of the objective optical system OBJ will be described.The aberration correcting element L1 and light converging element areplastic lenses. Further, in the periphery of respective optical functionsections (areas of the aberration correcting element L1 and the lightconverging element L2, through which the laser light flux from the blueviolet semiconductor laser LD1 passes), flange sections FL1 and FL2integrally molded with the optical function section, are provided, andwhen both of a part of flange sections FL1 and FL2 are mutuallyconnected, they are integrated.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, although graphicdisplay is neglected, divided into the 30-th optical function area AREA30 including the optical axis corresponding to an area in the numericalaperture 0.65 of DVD, and the 31-th optical function area AREA 31corresponding to an area from the numerical aperture 0.65 of DVD to thenumerical aperture 0.85 of the high density optical disk HD, and in the30-th optical function area AREA 30, the superposition type diffractivestructure HOE12, which is a structure in which a plurality ofring-shaped zones inside of which the step structure is formed, arearranged around the optical axis, is formed.

Because a structure of the superposition type diffractive structureHOE12 formed in the 30-th optical function area AREA 30 is the same asthe superposition type diffractive structure HOE4, the detaileddescription will be omitted herein.

Further, on the optical function surface S2 on the optical disk side ofthe aberration correcting element L1, although graphic display isneglected, the diffractive structure DOE13 structured by a plurality ofring-shaped zones whose sectional shape including the optical axis is asaw-toothed shape, is formed.

The diffractive structure DOE13 is a structure for suppressing the axialchromatic aberration of the objective optical system OBJ in the blueviolet area, and the spherical aberration following the temperaturechange, and the stepped section in the optical axis is designed so that,when the light flux of wavelength λ1=407 nm enters, +5-degree diffractedlight ray is generated in the diffraction efficiency of 100%. When thelight flux of wavelength λ2=660 nm enters into the diffractive structureDOE13, +3-degree diffracted light ray is generated in the diffractionefficiency of 99.8%, and the high diffraction efficiency can be securedalso for any wavelength.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source, and the type diffractive structure is formed on theoptical function surface S2 on the optical disk side, is applied,however, in contrast to this, a structure in which the type diffractivestructure is formed on the optical function surface S1 on thesemiconductor laser light source side, and the superposition typediffractive structure is formed on the optical function surface S2 onthe optical disk side, may also be applied.

Further, the liquid crystal phase control element LCD is structured by aliquid crystal layer by which the phase change is generated to thetransmitting light flux by the impression of voltage, an electrode layeropposing each other to impress the voltage on the liquid crystalelement, and a power source to supply the voltage to the electrodelayer.

At least one of the electrode layer opposing each other, is divided intoa predetermined pattern, and when the voltage is impressed on thiselectrode layer, the orientation condition of the liquid crystal elementis changed, and a predetermined phase can be added to the transmittinglight flux. Hereby, because the spherical aberration of a spot formed onthe information recording surface RL1 of the high density optical diskHD can be corrected, a good recording/reproducing characteristic can bealways maintained to the high density optical disk HD.

Causes of generation of the spherical aberration corrected by the liquidcrystal phase control element LCD are, for example, a wavelengthdispersion by the production error of the blue violet semiconductorlaser LD1, the refractive index change or refractive index distributionof the objective optical system OBJ following the temperature change, afocus-jump between layers at the time of recording/reproducing for themulti-layer disk such as 2-layer disk, 4-layer disk, and the thicknessdispersion or thickness distribution by the production error of theprotective layer PL1.

In the above description, a case where the spherical aberration of aspot formed on the information recording surface RL1 of the high densityoptical disk HD is corrected, is described, however, the sphericalaberration of a spot formed on the information recording surface RL2 ofDVD may also be corrected by the liquid crystal phase control elementLCD.

Further, the objective optical system OBJ and the liquid crystal phasecontrol element LCD are integrated through a connection member B.

Hereupon, the objective optical system OBJ in the present embodimenthas, in the same manner as the second optical pickup device PU2, thethird optical pickup device PU3, the fifth optical pickup device PU5,the seventh optical pickup device PU7, the aperture switching functioncorresponding to the numerical aperture NA2 of DVD, and by this apertureswitching function, the aperture switching corresponding to NA2, isconducted.

The Ninth Embodiment

FIG. 21 is a view generally showing a structure of the ninth opticalpickup device PU9 by which the recording/reproducing of the informationcan be adequately conducted also for any one of the high density opticaldisk, and DVD. The optical specification of the high density opticaldisk HD is the wavelength λ1=405 nm, the thickness t1 of the protectivelayer PL1=0.1 mm, numerical aperture NA1=0.85, the optical specificationof DVD is the wavelength λ2=650 nm, the thickness t2 of the protectivelayer PL2=0.6 mm, numerical aperture NA2=0.65. However, a combination ofthe wavelength, thickness of the protective layer, and numericalaperture is not limited to this.

The optical pickup device PU9 is structured by: the blue violetsemiconductor laser LD1 which is made to emit light when therecording/reproducing of the information is conducted for the highdensity optical disk HD and which projects the laser light flux of 405nm; red semiconductor laser LD2 laser which is made to emit light whenthe recording/reproducing of the information is conducted for DVD andwhich projects the laser light flux of 650 nm; light detector PD whichis commonly used for the high density optical disk HD and DVD; objectiveoptical system OBJ structured by the aberration correcting element L1and the light converging element L2 which has a function by which thelaser light fluxes transmitted this aberration correcting element L1 arelight converged on the information recording surfaces RL1, RL2, and bothsurfaces of which are aspherical surfaces; 2-axis actuator AC;wavelength selection filter WF; liquid crystal phase control elementLCD; 2-axis actuator AC; stop STO corresponding to the numericalaperture NA 0.85 of the high density optical disk HD; first polarizedbeam splitter BS1; second polarized beam splitter BS2; collimator lensCOL; 1-axis actuator UAC; sensor lens SEN; and beam shaping lens BS.

Hereupon, as the light source for the high density optical disk HD,other than the above blue violet semiconductor laser LD1, a blue violetSHG laser can also be used.

In the optical pickup device PU9, when the recording/reproducing of theinformation is conducted for the high density optical disk HD, as itsray of light path is drawn by a solid line in FIG. 21, the blue violetsemiconductor laser LD1 is made to emit light. The divergent light fluxprojected from the blue violet semiconductor laser LD1 is, whentransmits the beam shaping element SH, after its sectional shape isshaped from elliptical to circular, converted to parallel light flux bythe first collimator lens COL, after it transmits the first and secondpolarized beam splitters BS1, BS2, and the light flux diameter isregulated by stop STO, and it becomes a spot formed on the informationrecording surface RL1 through the protective layer PL1 of the highdensity optical disk HD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL1 is, after it transmits again theobjective optical system OBJ, and collimator lens COL, it is reflectedby the second polarized beam splitter BS2, and the astigmatism is givenby the sensor lens SEN and it is converted into the converged lightflux, and converged on the light receiving surface of the light detectorPD1. Then, by using the output signal of the light detector PD1, theinformation recorded in the high density optical disk HD can be read.

Further, in the optical pickup device PU9, when therecording/reproducing of the information is conducted for DVD, as itsray of light path is drawn by a dotted line in FIG. 21, the redsemiconductor laser LD2 is made to emit light. The divergent light fluxprojected from the red semiconductor laser LD2 is, after it is reflectedby the first polarized beam splitter BS1, it transmits the secondpolarized beam splitter BS2, and is converted to parallel light flux bythe collimator lens COL, and it becomes a spot formed on the informationrecording surface RL2 through the protective layer PL2 of DVD by theobjective optical system OBJ. The objective optical system OBJ conductsthe focusing and tracking by 2-axis actuator AC arranged in itsperiphery.

The reflected light flux modulated by the information pit on theinformation recording surface RL2, after it transmits again theobjective optical system OBJ, and collimator lens COL, it is reflectedby the second polarized beam splitter BS2, and the astigmatism is givenby the sensor lens SEN, and it is converted into the converged lightflux, and converged on the light receiving surface of the light detectorPD1. Then, by using the output signal of the light detector PD1, theinformation recorded in DVD can be read.

Next, a structure off the objective optical system OBJ will bedescribed. The aberration correcting element L1 is a plastic lens, andthe light converging element L2 is a glass lens. Further, the aberrationcorrecting element L1 and the light converging element L2 are integratedthrough a connection member B.

The optical function surface S1 on the semiconductor laser light sourceside of the aberration correcting element L1 is, although graphicdisplay is neglected, divided into the 32-th optical function area AREA32 including the optical axis corresponding to an area in the numericalaperture 0.65 of DVD, and the 33-th optical function area AREA 33corresponding to an area from the numerical aperture 0.65 of DVD to thenumerical aperture 0.85 of the high density optical disk HD, and in the32-th optical function area AREA 32, the superposition type diffractivestructure HOE13, which is a structure in which a plurality ofring-shaped zones inside of which the step structure is formed, arearranged around the optical axis, is formed.

Because the structure of the superposition type diffractive structureHOE13 formed in the 32-th optical function area AREA 32 is the same asthe superposition type diffractive structure HOE4 in the second opticalpickup device PU2, the detailed description will be omitted herein.

Further, on the optical function surface S2 on the optical disk side ofthe aberration correcting element L1, although graphic display isneglected, the diffractive structure DOE14 structured by a plurality ofring-shaped zones whose sectional shape including the optical axis is astep shape, is formed.

The diffractive structure-DOE14 is a structure for correcting thechromatic spherical aberration of the objective optical system OBJ inblue violet area, and the stepped section in the optical axis directionis designed so that, when the light flux of wavelength λ1=405 nm enters,+5-degree diffracted light ray is generated in the diffractionefficiency of 100%. When the light flux of wavelength λ2=650 nm entersinto the diffractive structure DOE14, +3-degree diffracted light ray isgenerated in the diffraction efficiency of 100%, and the highdiffraction efficiency is secured also for any wavelengths.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserlight source side, and type diffractive structure is formed on theoptical function surface S2 on the optical disk side, is applied,however, in contrast to this, a structure in which the type diffractivestructure is formed on the optical function surface S1 on thesemiconductor laser light source side, and the superposition typediffractive structure is formed on the optical function surface S2 onthe optical disk side, may also be applied.

Further, the collimator lens COL of the present embodiment is structuredso that its position can be shifted in the optical axis direction by the1-axis actuator UAC. Hereby, because the spherical aberration of a spotformed on the information recording surface RL1 of the high densityoptical disk HD can be corrected, a good recording/reproducingcharacteristic can be always maintained for the high density opticaldisk HD.

Causes of generation of the spherical aberration corrected by theposition adjustment of the collimator lens COL are, for example, awavelength dispersion by the production error of the blue violetsemiconductor laser LD1, the refractive index change or refractive indexdistribution of the objective optical system OBJ following thetemperature change, a focus-jump between layers at the time ofrecording/reproducing for the multi-layer disk such as 2-layer disk,4-layer disk, and the thickness dispersion or thickness distribution bythe production error of the protective layer PL1.

In the above description, a case where the spherical aberration of aspot formed on the information recording surface RL1 of the high densityoptical disk HD is corrected, is described, however, the sphericalaberration of a spot formed on the information recording surface RL2 ofDVD may also be corrected by the position adjustment of the collimatorlens COL.

Hereupon, the objective optical system OBJ in the present embodimenthas, in the same manner as the second optical pickup device PU2, thethird optical pickup device PU3, the fifth optical pickup device PU5,the seventh optical pickup device PU7, and the eighth optical pickupdevice PU8, the aperture switching function corresponding to thenumerical aperture NA2 of DVD, and by this aperture switching function,the aperture switching corresponding to NA2, is conducted.

The Tenth Embodiment

FIG. 22 is a view generally showing a structure of the tenth opticalpickup device PU10 by which the recording/reproducing of the informationcan be adequately conducted for any one of the high density opticaldisk, and DVD. The optical specification of the high density opticaldisk HD is the wavelength λ1=407 nm, the thickness t1 of the protectivelayer PL1=0.875 mm, numerical aperture NA1=0.85, and the opticalspecification of DVD is the wavelength λ2=660 nm, the thickness t2 ofthe protective layer PL2=0.6 mm, numerical aperture NA2=0.65. However, acombination of the wavelength, thickness of the protective layer, andnumerical aperture is not limited to this.

The optical pickup device PU10 is structured by: a laser module LM forthe high density optical disk/DVD structured by the first light emittingpoint EP1 which is made to emit light when the recording/reproducing ofthe information is conducted for the high density optical disk HD andwhich projects the laser light flux of 407 nm; the second light emittingpoint EP2 which is made to emit light when the recording/reproducing ofthe information is conducted for DVD and which projects the laser lightflux of 660 nm; first light receiving section DS1 which light-receivesthe reflected light flux from the information recording surface RL1 ofthe high density optical disk HD; second light receiving section DS2which light-receives the reflected light flux from the informationrecording surface RL2 of DVD; and prism PS; objective optical system OBJstructured by the aberration correcting element L1 and the lightconverging element L2 which has a function by which the laser light fluxtransmitted this aberration correcting element L1 is light converged oninformation recording surfaces RL1, RL2, and both surfaces of which areaspherical surfaces; 2-axis actuator AC; stop STO corresponding tonumerical aperture NA 0.85 of the high density optical disk HD;collimator lens COL; and 1-axis actuator UAC.

Hereupon, as the light source for the high density optical disk HD,other than the above-described blue violet semiconductor laser LD1, ablue violet SHG laser can also be used.

Further, in the optical pickup device PU110, when therecording/reproducing of the information is conducted for the highdensity optical disk HD, the first light emitting point EP1 is made toemit light. The divergent light flux projected from the first lightemitting point EP1 is, as its ray of light path is drawn by a solid linein FIG. 22, after reflected by the prism PS, it is converted intoparallel light flux by the collimator lens COL, and it becomes a spotformed on the information recording surface RL1 through the protectivelayer PL1 of the high density optical disk HD by the objective opticalsystem OBJ. The objective optical system OBJ conducts the focusing andtracking by 2-axis actuator AC arranged in its periphery. The reflectedlight flux modulated by the information pit on the information recordingsurface RL1 transmits again the objective optical system OBJ, andcollimator lens COL, and is reflected two times inside the prism PS, andlight-converged on the light receiving surface of the light detectorsection PD1. Then, by using the output signal of the light detectorsection PD1, the information recorded in the high density optical diskHD can be read.

Further, in the optical pickup device PU110, when therecording/reproducing of the information is conducted for DVD, thesecond light emitting point EP2 is made to emit light. The divergentlight flux projected from the second light emitting point EP2 is, as itsray of light path is drawn by a dotted line in FIG. 22, after reflectedby the prism PS, it transmits the collimator lens COL. Then, it entersinto the objective optical system OBJ as the divergent light, and itbecomes a spot formed on the information recording surface RL2 throughthe protective layer PL2 of DVD by the objective optical system OBJ. Theobjective optical system OBJ conducts the focusing and tracking by2-axis actuator AC arranged in its periphery. The reflected light fluxmodulated by the information pit on the information recording surfaceRL2 transmits again the objective optical system OBJ, and collimatorlens COL, and is reflected two times inside the prism PS, andlight-converged on the light detector section PD2. Then, by using theoutput signal of the light detector section PD2, the informationrecorded in DVD can be read.

Next, a structure of the objective optical system OBJ will be described.Both of aberration correcting element L1 and light converging element L2are plastic lenses. Further, in the periphery of respective opticalfunction sections (areas of the aberration correcting element L1 and thelight converging element L2, through which the laser light flux from theblue violet semiconductor laser LD1 passes), flange sections FL1 and FL2integrally molded with the optical function section, are provided, andwhen both of a part of flange sections FL1 and FL2 are mutuallyconnected, they are integrated.

The optical function surface S1 on the semiconductor laser light sourceside of the objective optical system OBJ is, although graphic display isneglected, divided into the 34-th optical function area AREA 34including the optical axis corresponding to an area in the numericalaperture 0.65 of DVD, and the 35-th optical function area AREA 35corresponding to an area from the numerical aperture 0.65 of DVD to thenumerical aperture 0.85 of the high density optical disk HD. Then, inthe 34-th optical function area AREA 34, the superposition typediffractive structure HOE14, which is a structure in which a pluralityof ring-shaped zones inside of which the step structure is formed, arearranged around the optical axis, is formed.

Because a structure of the superposition type diffractive structureHOE14 formed in the 34-th optical function area AREA 34 is the same asthe superposition type diffractive structure HOE4 in the second opticalpickup device PU2, the detailed description will be omitted herein.

On the optical function surface S2 on the optical disk side of theaberration correcting element L1, the optical path difference grantstructure NPS which is a structure for suppressing the sphericalaberration following the temperature change of the objective opticalsystem OBJ in the blue violet area, is formed. The stepped section inthe optical axis direction of this optical path difference grantstructure NPS is set to a depth in which, in the design referencetemperature of the objective optical system OBJ, 5-time optical pathdifferences are given to the light flux of wavelength λ1. When the lightflux of wavelength λ2 enters into the stepped section set to such adepth, because the optical path difference given to the light flux ofwavelength λ2 is 3 times of λ2, the high transmission factor is securedalso for any wavelength.

Because the optical path difference grant structure NPS has therefractive index dependency of the spherical aberration in which, whenthe refractive index is lowered, the spherical aberration changes in theunder correction direction, and when the refractive index is increased,the spherical aberration changes in the over correction direction, thespherical aberration change following the temperature change of theobjective optical system OBJ in the blue violet area, can be suppressed.

In the aberration correcting element L1 of the present embodiment, astructure in which the superposition type diffractive structure HOE14 isformed on the optical function surface S1 on the semiconductor laserlight source side, and the optical path difference grant structure NPSis formed on the optical function surface S2 on the optical disk side,is applied, however, in contrast to this, a structure in which theoptical path difference grant structure NPS is formed on the opticalfunction surface S1 on the semiconductor laser light source side, andthe superposition type diffractive structure HOE14 is formed on theoptical function surface S2 on the optical disk side, may also beapplied.

Further, the collimator lens COL of the present embodiment is structuredso that its position can be shifted in the optical axis direction by the1-axis actuator UAC. Hereby, because the spherical aberration of a spotformed on the information recording surface RL1 of the high densityoptical disk HD can be corrected, a good recording/reproducingcharacteristic can be always maintained for the high density opticaldisk HD.

Causes of generation of the spherical aberration corrected by theposition adjustment of the collimator lens COL are, for example, awavelength dispersion by the production error of the blue violetsemiconductor laser LD1, the refractive index change or refractive indexdistribution of the objective optical system OBJ following thetemperature change, a focus-jump between layers at the time ofrecording/reproducing for the multi-layer disk such as 2-layer disk,4-layer disk, and the thickness dispersion or thickness distribution bythe production error of the protective layer PL1.

In the above description, a case where the spherical aberration of aspot formed on the information recording surface RL1 of the high densityoptical disk HD is corrected, is described, however, the sphericalaberration of a spot formed on the information recording surface RL2 ofDVD may also be corrected by the position adjustment of the collimatorlens COL.

Hereupon, the objective optical system OBJ in the present embodimenthas, in the same manner as the second optical pickup device PU2, thethird optical pickup device PU3, the fifth optical pickup device PU5,the seventh optical pickup device PU7, the eighth optical pickup devicePU8, and the ninth optical pickup device PU9, the aperture switchingfunction corresponding to the numerical aperture NA2 of DVD, and by thisaperture switching function, the aperture switching corresponding toNA2, is conducted.

Eleventh Embodiment

FIG. 30 is a diagram showing schematically the structure of 11^(th)optical pickup device PU 11 that can conduct recording/reproducing ofinformation properly for any of high density optical disc HD, DVD andCD. In the optical specifications of the high density optical disc HD,wavelength λ1 is equal to 408 nm, thickness t1 of protective layer PL1is equal to 0.0875 mm and numerical aperture NA1 is equal to 0.85, inthe optical specifications of DVD, wavelength λ2 is equal to 658 nm,thickness t2 of protective layer PL2 is equal to 0.6 mm and numericalaperture NA2 is equal to 0.65, and in the optical specifications of CD,wavelength λ3 is equal to 785 nm, thickness t2 of protective layer PL3is equal to 1.2 mm and numerical aperture NA3 is equal to 0.45.

Optical pickup device PU11 is composed of laser module LM for highdensity optical disc HD/DVD/CD that is composed of light-emitting pointEP1 (first light source) that emits a laser light flux (first lightflux) with a wavelength of 408 nm which is emitted when conductingrecording/reproducing of information for high density optical disc HD,light-emitting point EP2 (second light source) that emits a laser lightflux (second light flux) with a wavelength of 658 nm which is emittedwhen conducting recording/reproducing of information for DVD,light-emitting point EP3 (second light source) that emits a laser lightflux (third light flux) with a wavelength of 785 nm which is emittedwhen conducting recording/reproducing of information for CD, firstlight-receiving section DS1 that receives reflected light flux comingfrom information recording surface RL1 of high density optical disc HD,second light-receiving section DS2 that receives reflected light fluxcoming from information recording surface RL2 of DVD, thirdlight-receiving section DS3 that receives reflected light flux comingfrom information recording surface RL3 of CD, and prism PS, objectiveoptical system (light-converging element) OBJ wherein a diffractivestructure (phase structure) is formed on its optical surface, and itsboth surfaces are asphericalal, aperture regulating element AP forDVD/CD, biaxial actuator AC for driving objective optical element OBJfor focusing/tracking, diaphragm STO corresponding to numerical apertureNA1 of high density optical disc HD, collimator lens COL, uniaxialactuator UAC that drives collimator lens COL in the optical axisdirection, liquid crystal phase control element LCD (sphericalaberration correcting means), and holding member B that integratesobjective optical system OBJ, aperture regulating element AP and liquidcrystal phase control element LCD solidly. In the present embodiment, anaberration correcting-element having a phase structure and alight-converging element which makes the first-third light fluxes toconverge light respectively on information recording surface RL1 of highdensity optical disc HD, information recording surface RL2 of DVD andinformation recording surface RL3 of CD are integrated solidly in thestructure.

In optical pickup device PU11, when conducting recording/reproducing ofinformation for high density optical disc HD, laser module LM isoperated to make the first light-emitting point EP1 to emit light. Adivergent light flux emitted from the first light-emitting point EP1 isreflected by prism PS as its light path is drawn with solid lines inFIG. 30, then, it passes through collimator lens COL to be convertedinto a parallel light flux, then, the parallel light flux is regulated,in terms of its diameter, by diaphragm STO, and it passes through liquidcrystal phase control element LCD and aperture regulating element AP tobecome a spot formed on information recording surface RL1 by objectiveoptical system OBJ through the first protective layer PL1. The objectiveoptical system OBJ conducts focusing and tracking with biaxial actuatorAC1 arranged around the objective optical system OBJ. The reflectedlight flux modulated by information pits on information recordingsurface RL1 passes again through objective optical system OBJ, apertureregulating element AP and liquid crystal phase control element LCD to beconverted into a converged light flux by collimator lens COL, and isreflected twice in prism PS to be converged on light-receiving sectionDS1. Then, information recorded in high density optical disc HD can beread by using output signals of the light-receiving section DS1.

In optical pickup device PU11, when conducting recording/reproducing ofinformation for DVD, collimator lens COL is moved by uniaxial actuatorUAC so that a distance between objective optical system OBJ andcollimator lens COL may be smaller than that in the case of conductingrecording/reproducing of information for high density optical disc HD,so that the second light flux may emerge from collimator lens COL underthe state of a parallel light flux. After that, laser module LM isoperated to make the second light-emitting point EP2 to emit light. Adivergent light flux emitted from the second light-emitting point EP2 isreflected by prism PS as its light path is drawn with dotted lines inFIG. 30, then, it passes through collimator lens COL to be convertedinto a parallel light flux, then, the parallel light flux passes throughliquid crystal phase control element LCD and is regulated, in terms ofits diameter, by aperture regulating element AP to become a spot formedon information recording surface RL2 by objective optical system OBJthrough the second protective layer PL2. The objective optical systemOBJ conducts focusing and tracking with biaxial actuator AC1 arrangedaround the objective optical system OBJ. The reflected light fluxmodulated by information pits on information recording surface RL2passes again through objective optical system OBJ, aperture regulatingelement AP and liquid crystal phase control element LCD to be convertedinto a converged light flux by collimator lens COL, and is reflectedtwice in prism PS to be converged on light-receiving section DS2. Then,information recorded in DVD can be read by using output signals of thelight-receiving section DS2.

When conducting recording/reproducing of information for CD in opticalpickup device PU11, liquid crystal phase control element LCD is operatedin a way that spherical aberration in the direction toward insufficientcorrection may be added to the third light flux that passes through theliquid crystal phase control element LCD, for correcting sphericalaberration caused by a difference between thickness t1 of protectivelayer PL1 and thickness t3 of protective layer PL3. After that, lasermodule LM is operated to make the third light-emitting point EP3 to emitlight. A divergent light flux emitted from the third light-emittingpoint EP3 is reflected by prism PS as its light path is drawn withtwo-dot chain lines in FIG. 30, then, it passes through collimator lensCOL to be converted into a parallel light flux, then, the parallel lightflux passes through liquid crystal phase control element LCD to be givenspherical aberration in the direction toward insufficient correction,and is regulated, in terms of its diameter, by aperture regulatingelement AP to become a spot formed on information recording surface RL3by objective optical system OBJ through the third protective layer PL3.The objective optical system OBJ conducts focusing and tracking withbiaxial actuator AC1 arranged around the objective optical system OBJ.The reflected light flux modulated by information pits on informationrecording surface RL3 passes again through objective optical system OBJ,aperture regulating element AP and liquid crystal phase control elementLCD to be converted into a converged light flux by collimator lens COL,and is reflected twice in prism PS to be converged on light-receivingsection DS3. Then, information recorded in CD can be read by usingoutput signals of the light-receiving section DS3.

Incidentally, in the same way as in the case of DVD, it is also possibleto arrange so that collimator lens COL is moved by uniaxial actuator UACso that a distance between objective optical system OBJ and collimatorlens COL may be smaller than that in the case of conductingrecording/reproducing of information for high density optical disc HD,so that the third light flux may emerge from collimator lens COL underthe state of a parallel light flux.

Next, the structure of the objective optical system OBJ will beexplained as follows. Diffractive structure DOE15 (its section is in aserrated form) formed on an optical surface on the laser module side LMis a structure to correct spherical aberration caused by a differencebetween thickness t1 of protective layer PL1 and thickness t2 ofprotective layer PL2. The objective optical system OBJ converges primarydiffracted light ray of the first-third light fluxes generated bydiffractive structure DOE15 respectively on information recordingsurface RL1 of high density optical disc HD, information recordingsurface RL2 of DVD and information recording surface RL3 of CD. Sincethe optical path difference function of the diffractive structure DOE15is optimized so that spherical aberration caused by a difference betweenthickness t1 of protective layer PL1 and thickness t2 of protectivelayer PL2 may be corrected, spherical aberration caused by a differencebetween thickness t1 of protective layer PL1 and thickness t3 ofprotective layer PL3 cannot be corrected completely, and some sphericalaberrations remain. In the present embodiment, however, compatibilitybetween high density disc HD and CD is attained by correcting theresidual spherical aberration with liquid crystal phase control elementLCD.

The collimator lens COL in the present embodiment is constructed so thatits position may be moved in the optical axis direction by uniaxialactuator UAC, which makes it possible to correct spherical aberration ofa spot formed on information recording surface RL1 of high densityoptical disc HD. Causes for generation of spherical aberration correctedby position adjustment of the collimator lens COL include, for example,wavelength dispersion caused by manufacturing errors for the first lightsource, refractive index changes and refractive index distribution ofobjective optical system OBJ resulted from temperature changes, focusjump between layers in recording/reproducing for multi-layer disc suchas 2-layer disc and 4-layer disc, and thickness dispersion and thicknessdistribution resulting from manufacturing errors for protective layerPL1.

In the explanation above, there has been described an occasion wherespherical aberration of a spot formed on information recording surfaceRL1 of high density optical disc HD was corrected, spherical aberrationof a spot formed on information recording surface RL2 of DVD may also becorrected by position adjustment for collimator lens COL.

Twelfth Embodiment

FIG. 31 is a diagram showing schematically the structure of 12^(th)optical pickup device PU12 that can conduct recording/reproducingproperly for any of high density optical disc HD, DVD and CD. In theoptical specifications of the high density optical disc HD, wavelengthλ1 is equal to 408 nm, thickness t1 of protective layer PL1 is equal to0.0875 mm and numerical aperture NA1 is equal to 0.85, in the opticalspecifications of DVD, wavelength λ2 is equal to 658 nm, thickness t2 ofprotective layer PL2 is equal to 0.6 mm and numerical aperture NA2 isequal to 0.65, and in the optical specifications of CD, wavelength λ3 isequal to 785 nm, thickness t2 of protective layer PL3 is equal to 1.2 mmand numerical aperture NA3 is equal to 0.45. However, a combination ofthe wavelength, a thickness of a protective layer and a numericalaperture is not limited to the foregoing.

Optical pickup device PU11 is composed of laser module LM for highdensity optical disc HD/DVD/CD that is composed of light-emitting pointEP1 (first light source) that emits a laser light flux (first lightflux) with a wavelength of 408 nm which is emitted when conductingrecording/reproducing of information for high density optical disc HD,light-emitting point EP2 (second light source) that emits a laser lightflux (second light flux) with a wavelength of 658 nm which is emittedwhen conducting recording/reproducing of information for DVD,light-emitting point EP3 (second light source) that emits a laser lightflux (third light flux) with a wavelength of 785 nm which is emittedwhen conducting recording/reproducing of information for CD, firstlight-receiving section DS1 that receives reflected light flux comingfrom information recording surface RL1 of high density optical disc HD,second light-receiving section DS2 that receives reflected light fluxcoming from information recording surface RL2 of DVD, thirdlight-receiving section DS3 that receives reflected light flux comingfrom information recording surface RL3 of CD, and prism PS, objectiveoptical system (light-converging element) OBJ composed of aberrationcorrecting element L1 having on its optical surface the superposeddiffractive structure (phase structure) and a diffractive structure(second diffractive structure) and of light-converging element L2 whoseboth surfaces are asphericalal, aperture regulating element AP for CD,biaxial actuator AC for driving objective optical element OBJ forfocusing/tracking, diaphragm STO corresponding to numerical aperture NA1of high density optical disc HD, collimator lens COL, expander lens EXP(aspherical surface correcting means) composed of negative lens E1 andpositive lens E2, uniaxial actuator UAC that drives negative lens E1 inthe optical axis direction and holding member B that integratesobjective optical system OBJ and aperture regulating element AP solidly.

In optical pickup device PU12, when conducting recording/reproducing ofinformation for high density optical disc HD, laser module LM isoperated to make the first light-emitting point EP1 to emit light. Adivergent light flux emitted from the first light-emitting point EP1 isreflected by prism PS as its light path is drawn with solid lines inFIG. 31, then, it passes through collimator lens COL to be convertedinto a parallel light flux, then, the parallel light flux passes throughexpander lens EXP to be enlarged in terms of a light flux diameter, thenis regulated, in terms of its diameter, by diaphragm STO, and it passesthrough aperture regulating element AP to become a spot formed oninformation recording surface RL1 by objective optical system OBJthrough first protective layer PL1. The objective optical system OBJconducts focusing and tracking with biaxial actuator AC1 arranged aroundthe objective optical system OBJ. The reflected light flux modulated byinformation pits on information recording surface RL1 passes againthrough objective optical system OBJ, aperture regulating element AP andexpander lens EXP to be converted into a converged light flux bycollimator lens COL, and is reflected twice in prism PS to be convergedon light-receiving section DS1. Then, information recorded in highdensity optical disc HD can be read by using output signals of thelight-receiving section DS1.

In optical pickup device PU12, when conducting recording/reproducing ofinformation for DVD, negative lens E1 is moved by uniaxial actuator UACso that a distance between negative lens E1 and positive lens E2 may belarger than that in the case of conducting recording/reproducing ofinformation for high density optical disc HD, so that the second lightflux may emerge from expander lens EXP under the state of a parallellight flux. After that, laser module LM is operated to make the secondlight-emitting point EP2 to emit light. A divergent light flux emittedfrom the second light-emitting point EP2 is reflected by prism PS as itslight path is drawn with dotted lines in FIG. 31, then, it passesthrough collimator lens COL to be converted into a parallel light flux,then, the parallel light flux passes through expander lens EXP to beenlarged in terms of a diameter of the light flux, and it becomes a spotformed on information recording surface RL2 by objective optical systemOBJ through the second protective layer PL2, after passing through theaperture regulating element AP. The objective optical system OBJconducts focusing and tracking with biaxial actuator AC1 arranged aroundthe objective optical system OBJ. The reflected light flux modulated byinformation pits on information recording surface RL2 passes againthrough objective optical system OBJ, aperture regulating element AP andexpander lens EXP to be converted into a converged light flux bycollimator lens COL, and is reflected twice in prism PS to be convergedon light-receiving section DS2. Then, information recorded in DVD can beread by using output signals of the light-receiving section DS2.

In optical pickup device PU12, when conducting recording/reproducing ofinformation for CD, negative lens E1 is moved by uniaxial actuator UACso that a distance between negative lens E1 and positive lens E2 may besmaller than that in the case of conducting recording/reproducing ofinformation for high density optical disc HD, so that sphericalaberration resulted from a difference between thickness t1 of protectivelayer PL1 and thickness t3 of protective layer PL3 may be corrected.After that, laser module LM is operated to make the third light-emittingpoint EP3 to emit light. A divergent light flux emitted from the thirdlight-emitting point EP3 is reflected by prism PS as its light path isdrawn with two-dot chain lines in FIG. 31, then, it passes throughcollimator lens COL to be converted into a substantially parallel lightflux, then, the parallel light flux passes through expander lens EXP tobe converted into divergent light flux and it becomes a spot formed oninformation recording surface RL3 by objective optical system OBJthrough the third protective layer PL3, after being regulated by theaperture regulating element AP in terms of a light flux diameter. Theobjective optical system OBJ conducts focusing and tracking with biaxialactuator AC1 arranged around the objective optical system OBJ. Thereflected light flux modulated by information pits on informationrecording surface RL3 passes again through objective optical system OBJ,aperture regulating element AP and expander lens EXP to be convertedinto a converged light flux by collimator lens COL, and is reflectedtwice in prism PS to be converged on light-receiving section DS3. Then,information recorded in CD can be read by using output signals of thelight-receiving section DS3.

Next, the structure of objective optical element OBJ will be explained.Each of aberration correcting element L1 and light-converging element L2is a plastic lens, and when flange portion FL1 and flange portion FL2each being formed to be solid with an optical functional portion of theplastic lens are cemented each other, they are integrated solidly.Superposed type structure HOE15 formed on an optical surface ofaberration correcting element L1 on the part of laser module LM is astructure to correct spherical aberration caused by a difference betweenthickness t1 of protective layer PL1 and thickness t2 of protectivelayer PL2. Since its specific structure and functions are the same asthose of the superposed type diffractive structure HOE4 in the secondoptical pickup device PU2, detailed explanation for them will be omittedhere. Incidentally, since the superposed type structure HOE15 is formedin only numerical aperture NA2 of DVD, the second light flux that passesthrough the area outside NA2 becomes a flare component on informationrecording surface RL2 of DVD, and aperture restriction for DVD iscarried out automatically, in the structure.

Further, the objective optical system OBJ makes 5^(th) order diffractedlight ray of the first light flux, 3^(rd) order diffracted light ray ofthe second light flux and 2^(nd) order diffracted light ray of the thirdlight flux which are generated on diffractive structure DOE16 (itssectional view is a staircase form) formed on an optical surface ofaberration correcting element L1 on the part of the optical disc to beconverged respectively on information recording surface RL1 of highdensity optical disc, information recording surface RL2 of DVD and oninformation recording surface RL3 of CD. This diffractive structureDOE16 is a structure to reduce spherical aberration caused by adifference between t1 and t3 by adding to the third light flux anoptical path difference that is a half integer multiple of λ3. Owing tothis, it is possible to prevent that an absolute value of magnificationm3 of objective optical system OBJ to the third light flux in the caseof conducting recording/reproducing of information for CD becomes toogreat, thus, an amount of movement of negative lens E1 can be small, andtracking characteristics of objective optical system OBJ can be madeexcellent.

In the structure of the present embodiment, spherical aberration of thespot formed on information recording surface RL1 of high density opticaldisc HD is corrected when moving negative lens E1 is moved in theoptical axis direction by uniaxial actuator UAC. Causes for generationof spherical aberration to be corrected by positional adjustment ofnegative lens E1 include, for example, wavelength dispersion caused bymanufacturing errors of the first light source, refractive index changesand refractive index distribution of objective optical system OBJresulting from temperature changes, focus jump between layers in thecase of conducting recording/reproducing for multi-layer disc such as2-layer disc and 4-layer disc and thickness dispersion and thicknessdistribution caused by manufacturing errors for protective layers PL1.

There has been explained an occasion wherein spherical aberration of aspot formed on information recording surface RL1 of high density opticaldisc HD is corrected. However, it is also possible to arrange so thatspherical aberration of a spot formed on information recording surfaceRL2 of DVD may be corrected by positional adjustment of negative lensE1. Further, it is possible to employ the structure wherein positivelens E2 is moved in place of negative lens E1.

Further, it is possible to use, as asphericalal aberration correctingmeans, a collimator lens and a coupling lens which can be moved in theoptical axis direction by an actuator, in place of expander lens EXP.

Next, 8 examples (Example 1-8) of an optical element preferable as theobjective optical system OBJ of the above-described optical pickupdevices PI1-PU4, PU8-PU10, will be described by listing specific numeralvalues.

The aspherical surface of optical surface on which the superpositiontype diffraction strcuture and diffraction strcuture in each example areformed, is expresed by an arithmetic expression, that is, the followingArith-5, into which coefficients in Table 15-Table 22 are substituted,when the deformation amount from the plane tangent to an apex of theplane, is X (mm), the height in the direction perpendicular to theoptical axis is h (mm), and radius of curvature is r (mm). Where, κ is aconical coefficient, and A2 i is an aspherical surface coefficient.

$\begin{matrix}{x = {\frac{h^{2}/r}{1 + \sqrt{1 - {( {1 + \kappa} )( {h/r} )^{2}}}} + {\sum\limits_{i = 2}\; {A_{2i}h^{2i}}}}} & ( {{Arith}\text{-}5} )\end{matrix}$

Further, the superpositon type diffractive structure and the diffractivestructure in each example are expressed by the optical path differenceadded to transmission wave-front by these structures. Such an opticalpath difference is expressed by the optical path difference function φb(mm) defined by the above-described Arith-1, when λ is the wavelength ofthe incident light flux, λB is production wavelength, height in thedirection perpendicular to the optical axis is h (mm), B2 j is anoptical path difference function coefficient, and n is the diffractionorder.

In Table 15-Table 25, NA1, f1, λ1, m1 and t1 represent respectively anumerical aperture of objective optical system OBJ in the case of usinghigh density optical disc HD, a focal length of the objective opticalsystem OBJ, a wavelength of the objective optical system OBJ, amagnification of the objective optical system OBJ, and a thickness of aprotective layer, while, NA2, f2, λ2, m2 and t2 represent the samevalues in the case of using DVD and NA3, f3, λ3, m3 and t3 represent thesame values in the case of using CD.

Further, r (mm) represents a radius of curvature, d1 (mm), d2 (mm) andd3 (mm) represent lens distances respectively in the case of using highdensity optical disc HD, DVD and CD, Nλ1, Nλ2 and Nλ3 represent lensdiffractive indexes respectively for wavelength λ1, wavelength λ2 andwavelength λ3, while, νd represents Abbe's number of the lens for dline.

Further, n1, n2 and n3 represent diffraction orders of diffracted raysof light respectively for the first, second and third light fluxesgenerated by a superposed type diffractive structure and a diffractivestructure.

In the optical element of Examples 1 to 3, the light converging elementL2 which is a plastic lens whose numerical aperture is 0.85, in whichthe spherical aberration correction is optimized to the wavelength 408nm, thickness of the protective layer 0.0875 mm, and magnification1/18.215, is combined with the aberration correcting element L2 which isa plastic lens in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserside, and the diffractive structure is formed on the optical functionsurface S2 on the optical disk side.

In the optical element of Example 4, the light converging element L2which is a plastic lens whose numerical aperture is 0.85, in which thespherical aberration correction is optimized to the wavelength 408 nm,thickness of the protective layer 0.0875 mm, and magnification 1/17.123,is combined with the aberration correcting element L2 which is a plasticlens in which the superposition type diffractive structure is formed onthe optical function surface S1 on the semiconductor laser side, and thediffractive structure is formed on the optical function surface S2 onthe optical disk side.

Further, in the optical element of Example 5, the light convergingelement L2 which is a glass lens whose numerical aperture is 0.85, inwhich the spherical aberration correction is optimized to the wavelength408 nm, thickness of the protective layer 0.0875 mm, and magnification0, is combined with the aberration correcting element L2 which is aplastic lens in which the superposition type diffractive structure isformed on the optical function surface S1 on the semiconductor laserside, and the diffractive structure is formed on the optical functionsurface S2 on the optical disk side.

In the optical element of Example 6, the light converging element L2which is a plastic lens whose numerical aperture is 0.85, in which thespherical aberration correction is optimized to the wavelength 407 nm,thickness of the protective layer 0.0875 mm, and magnification 1/14.104,is combined with the aberration correcting element L1 which is a plasticlens in which the superposition type diffractive structure is formed onthe optical function surface S1 on the semiconductor laser side, and thediffractive structure is formed on the optical function surface S2 onthe optical disk side.

In the optical element of Example 7, the light converging element L2which is a glass lens whose numerical aperture is 0.85, in which thespherical aberration correction is optimized to the wavelength 4.05 nm,thickness of the protective layer 0.1 mm, and magnification 0, iscombined with the aberration correcting element L1 which is a plasticlens in which the superposition type diffractive structure is formed onthe optical function surface Si on the semiconductor laser side, and thediffractive structure is formed on the optical function surface S2 onthe optical disk side.

In the optical element of Example 8, the light converging element L2which is a glass lens whose numerical aperture is 0.85, in which thespherical aberration correction is optimized to the wavelength 407 nm,thickness of the protective layer 0.0875 mm, and magnification 1/11.416,is combined with the aberration correcting element L1 which is a plasticlens in which the optical path difference grant structure NPS is formedon the optical function surface S1 on the semiconductor laser side, andthe superposition type diffractive structure HOE is formed on theoptical function surface S2 on the optical disk side.

Example 1

The optical element of Example 1 is an optimum optical element as theobjective optical system OBJ of the first optical pickup device PU1 asshown in FIG. 1, and its specific numerical value data is shown in Table15.

TABLE 15 (Example 1) (Optical specification) HD: NA1 = 0.85, f1 = 2.200mm, λ1 = 408 nm, m1 = 0, t1 = 0.0875 mm DVD: NA2 = 0.60, f2 = 2.287 mm,λ2 = 658 nm, m2 = −1/8.104, t2 =0.6 mm CD: NA3 = 0.45, f3 2.281 mm, λ3 =785 nm, m3 = 1/8.032, t3 = 1.2 mm (Paraxial data) Surface d1 d2 d3 No.r(mm) (mm) (mm) (mm) Nλ1 Nλ2 Nλ3 vd OBJ ∞ 19.680 19.466 STO 10.050 0.0500.050 1 (lower 0.900 0.900 0.900 1.52424 1.50643 1.50497 56.5 table) 2(lower 0.050 0.050 0.050 table) 3 1.442 2.510 2.510 2.510 1.559651.54062 1.53724 56.3 4 −4.596 0.684 0.720 0.334 5 ∞ 0.0875 0.600 1.2001.62110 1.57975 1.57326 30.0 6 ∞ (Paraxial radius of curvature of the1st surface and 2nd surface, aspherical surface coefficient, diffractionorder, production wavelength, optical path difference functioncoefficient) The 1st surface The 2nd surface AREA1 AREA2 AREA3 AREA4AREA5 (0 ≦ h ≦ 1.10) (1.10 ≦ h ≦ 1.40) (1.40 ≦ h) (0 ≦ h ≦ 1.45) (1.45 ≦h) r −133.777 −179.615 −97.345 −391.560 5742.431 κ 0 0 0 0 0 A41.6642E−03 −4.9735E−04 8.5644E−04 3.7997E−03 9.0524E−04 A6 −2.9440E−03−1.5451E−03 −4.5098E−04 −1.6029E−03 2.2495E−04 A8 1.1591E−03 1.1728E−032.5259E−04 3.0156E−04 2.5769E−04 A10 0 −1.9139E−04 −2.7080E−051.5420E−04 5.0597E−06 n1/n2/n3 0/+1/0 0/−1/−2 0/−2/±3 +2/+1/+1 +2/+1/+1λB 658 nm 658 nin. 658 nm 390 nm 408 nm B2 0 0 0 −6.6500E−03 −7.4212E−03B4 −1.4058E−03 1.8254E−03 9.1200E−04 −4.1697E−04 −3.4132E−04 B62.5969E−03 −3.2646E−03 0 −6.1147E−04 −1.2010E−05 B8 −1.4389E−031.6818E−03 0 4.8077E−04 −3.7652E−05 B10 4.2555E−04 −4.0655E−04 0−1.2778E−04 −2.9101E−06 (aspherical surface coefficient of the 3rdsurface and the 4th surface) 3rd surface 4th surface κ −6.6181E−01−1.6733E+02 A4 1.1149E−02 1.0501E−01 A6 2.4988E−03 −1.1650E−01 A81.8506E−05 1.0619E−01 A10 2.9476E−04 −7.0978E−02 A12 6.5641E−052.7327E−02 A14 −4.2096E−05 −4.3888E−03 A16 −3.6165E−06 A18 7.9919E−06A20 −1.2231E−06

By the action of the superposition type diffractive structure HOE1formed in the first optical function area AREA 1, while themagnification m2 to the wavelength λ2 and the magnification m3 to thewavelength λ3 are made almost coincident, the spherical aberration dueto the difference of thickness between protective layers of the highdensity optical disk and DVD is corrected. Further, the superpositiontype diffractive structure HOE2 formed in the second optical functionarea AREA 2 and the superposition type diffractive structure HOE3 formedin the third optical function area AREA 3 function in the same manner asthe dichroic filter when the recording/resproducing of the informationis conducted for DVD or CD, and the aperture limit is automaticallyconducted.

Further, by the action of the diffractive structure DOE1 formed in thefourth optical function area AREA 4 and the diffractive structure DOE2formed in the fifth optical function area AREA 5, the chromaticaberration in the blue violet area and the spherical aberrationfollowing the incident wavelength change are corrected.

When the wavelength change amount of the blue violet semiconductor laserLD1 by the mode-hopping, is assumed as +1 nm, to the change amount 151mλ RMS of the defocus component in only the light converging element L2,when the light converging element L2 and the aberration correctingelement L1 are combined, it becomes 20 mλ RMS, and it can be seen thatthe change of defocus component by the mode-hopping can be finelycorrected.

Further, when the wavelength dispersion by the production error of theblue violet semiconductor laser LD1 is assumed as +10 nm, to the changeamount 74 mλ RMS of the spherical aberration component in only the lightconverging element L2, when the light converging element L2 and theaberration correcting element L1 are combined, it becomes 4 mλ RMS, andit can be seen that the spherical aberration change following theincident wavelength change can be finely corrected.

Example 2

An optical element of Example 2 is an optimum optical element as theobjective optical system OBJ of the second optical pickup device PU2 asshown in FIG. 3 and the fifth optical pickup device PU5 as shown in FIG.14, and its specific numeric value data will be shown in Table 16.

TABLE 16 (Example 2) (Optical specification of the optical element) HD:NA1 = 0.85, f1 = 2.200 mm, λ1 = 408 nm, m1 = 0, t1 = 0.0875 mm DVD: NA2= 0.67, f2 = 2.282 mm, λ2 = 658 nm, m2 = 0, t2 = 0.6 mm CD: NA3 = 0.45,f3 = 2.281 mm, λ3 = 785 nm, m3 = −1/8.097, t3 = 1.2 mm (Paraxial data ofthe optical element) Surface d1 d2 d3 No. r(mm) (mm) (mm) (mm) Nλ1 Nλ2Nλ3 νd OBJ ∞ ∞ 19.617 STO 0.050 0.050 0.050 1 (lower 0.900 0.900 0.9001.52424 1.50643 1.50497 56.5 table) 2 (lower 0.050 0.050 0.050 table) 31.442 2.510 2.510 2.510 1.55965 1.54062 1.53724 56.3 4 −4.596 0.6840.432 0.331 5 ∞ 0.0875 0.600 1.200 1.62110 1.57975 1.57326 30.0 6 ∞(Paraxial data of the optical element + coupling lens) Surface No. r(mm) d3 (mm) Nλ3 νd OBJ 7.000  1′ −9.315 2.000 1.50497 56.5  2′ −7.8197.000 STO 0.050 1 (lower 0.900 1.50497 56.5 table) 2 (lower 0.050 table)3 1.442 2.510 1.53724 56.3 4 −4.596 0.355 5 ∞ 1.200 1.57326 30.0 6 ∞(Paraxial radius of curvature of the 1st surface and 2nd surface,aspherical surface coefficient, diffraction order, productionwavelength, optical path difference function coefficient) The 1stsurface The 2nd surface AREA6 AREA 7 AREA 8 AREA 9 (0 ≦ h ≦ 1.55) (1.55≦ h) (0 ≦ h ≦ 1.53) (1.53 ≦ h) r −113.707 −70.279 −57.498 −56.666 κ 0 00 9.6772E+01 A4 −3.0576E−03 −5.0921E−04 −1.7128E−03 1.6692E−03 A61.0766E−03 2.6280E−04 3.2682E−03 4.4185E−04 A8 0 1.4914E−04 −8.1260E−042.0756E−04 A10 0 −2.3320E−05 1.7830E−04 1.0485E−05 n1/n2/n3 0/+1/0 —+2/+1/+1 +2/+1/+1 λB 658 nm — 390 nm 408 nm B2 0 0 −4.9000E−03−5.8114E−03 B4 −1.0292E−03 0 −3.5147E−04 −5.3146E−04 B6 −2.8510E−04 0−5.2410E−04 −7.0255E−05 B8 2.3248E−05 0 1.9011E−04 −6.7478E−06 B10−1.0191E−05 0 −4.2545E−05 −9.9430E−06 (Aspherical surface coefficient ofthe 3rd surface and the 4th surface) 3rd surface 4th surface κ−6.6181E−01 −1.6733E+02 A4 1.1149E−02 1.0501E−01 A6 2.4988E−03−1.1650E−01 A8 1.8506E−05 1.0619E−01 A10 2.9476E−04 −7.0978E−02 A126.5641E−05 2.7327E−02 A14 −4.2096E−05 −4.3888E−03 A16 −3.6165E−06 A187.9919E−06 A20 −1.2231E−06 (Aspherical surface coefficient of the 2nd′surface) The 2′ surface κ 0 A4 −2.2210E−02 A6 9.0770E−02 A8 −1.4749E−01A10 9.3254E−02

By the action of the superposition type diffractive structure HOE4(HOE8) formed in the sixth (18th) optical function area AREA 6 (AREA18), while the magnification m1 to the wavelength λ1 and themagnification m2 to the wavelength λ2 are made almost coincident witheach other, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected.

Further, by the action of the diffractive structure DOE3 (DOE8) formedin the 8th (the 20th) optical function area AREA 8 (AREA 20) and thediffractive structure DOE4 (DOE9) formed in the 9th (the 21st) opticalfunction area AREA 9 (AREA 21), the chromatic aberration in the blueviolet area and the spherical aberration following the environmentaltemperature change are corrected.

When the wavelength change amount of the blue violet semiconductor laserLD1 by the mode-hopping, is assumed as +1 nm, to the change amount 151mλ RMS of the defocus component in only the light converging element L2,when the light converging element L2 and the aberration correctingelement L1 are combined, it becomes 27 mλ RMS, and it can be seen thatthe change of defocus component by the mode-hopping can be finelycorrected.

Further, in the case where the environmental temperature rises by 30°C., when the oscillation wavelength of the blue violet semiconductorlaser is 409.5 nm, the refractive index of the aberration correctingelement at the time, is 1.52079, and the refractive index of the lightconverging element L2 is 1.55671, to the change amount 116 mλ RMS of thespherical aberration component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 45 mλ RMS, and it can be seen that thespherical aberration change following the environmental temperaturechange, is finely corrected.

Further, in Table 16, the numeric data when the optical element of thepresent Example is combined with the coupling lens CUL as the comacorrecting element, is also shown. When a shift amount in the directionperpendicular to the optical axis of the optical element when therecording/reproducing of the information is conducted for CD, is 0.2 mm,to the generation amount 51 mλ RMS of the coma in only the opticalelement, when the light converging element L2 is combined with theaberration correcting element L1, it becomes 20 mλRMS, and it can beseen that the coma change following the shift of the optical element isfinely corrected.

Example 3

An optical element of Example 3 is an optimum optical element as theobjective optical system OBJ of the third optical pickup device as shownin FIG. 5, and its specific numeric data is shown in Table 17.

TABLE 17 (Example 3) (Optical specification of the optical element) HD:NA1 = 0.85, f1 = 2.200 mm, λ1 = 408 nm, m1 = 0, t1 = 0.0875 mm DVD: NA2= 0.67, f2 = 2.282 mm, λ2 = 658 nm, m2 = −1/16.051, t2 = 0.6 mm CD: NA3= 0.51, f3 = 2.281 mm, λ3 = 785 nm, m3 = −1/8.100, t3 = 1.2 mm (Paraxialdata of the optical element) Surface d1 d2 d3 No. r(mm) (mm) (mm) (mm)Nλ1 Nλ2 Nλ3 νd OBJ ∞ 37.788 19.623 STO 0.050 0.050 0.050 1 (lower 0.9000.900 0.900 1.52424 1.50643 1.50497 56.5 table) 2 (lower 0.050 0.0500.050 table) 3 1.442 2.510 2.510 2.510 1.55965 1.54062 1.53724 56.3 4−4.596 0.684 0.575 0.331 5 ∞ 0.0875 0.600 1.200 1.62110 1.57975 1.5732630.0 6 ∞ (Paraxial data of the optical element + coupling lens) SurfaceNo. r (mm) d2 (mm) d3 (mm) Nλ2 Nλ3 νd OBJ 15.000 15.000  1′ ∞ 2.0002.000 1.50643 1.50497 56.5  2′ −19.617 9.723 10.000 STO 0.050 0.050 1(lower 0.900 0.900 1.50643 1.50497 56.5 table) 2 (lower 0.050 0.050table) 3 1.442 2.510 2.510 1.54062 1.53724 56.3 4 −4.596 0.573 0.296 5 ∞0.600 1.200 1.57975 1.57326 30.0 6 ∞ (Paraxial radius of curvature ofthe 1st surface and 2nd surface, aspherical surface coefficient,diffraction order, production wavelength, optical path differencefunction coefficient) The 1st surface The 2nd surface AREA 10 AREA 11AREA 12 AREA 13 (0 ≦ h ≦ 1.53) (1.53 ≦ h) (0 ≦ h ≦ 1.55) (1.55 ≦ h) r−115.962 −49.346 −60.675 −53.087 κ 0 0 0 9.6672E+01 A4 −2.7281E−033.1345E−03 −1.4250E−03 1.6926E−03 A6 9.9643E−04 −9.2118E−04 1.9093E−035.7031E−04 A8 0 2.4236E−05 5.0795E−05 1.1423E−04 A10 0 −1.6729E−06−1.9371E−06 2.3835E−05 n1/n2/n3 0/+1/0 — +2/+1/+1 +2/+1/+1 λB 658 nm —390 nm 408 nm B2 0 0 −5.0000E−03 −5.8988E−03 B4 −5.0409E−04 0−3.3959E−04 −3.8146E−04 B6 1.2618E−04 0 −2.0605E−04 1.9458E−05 B8−4.3226E−05 0 −2.5093E−05 −6.1471E−05 B10 −5.0031E−06 0 2.4650E−06−2.4896E−06 (Aspherical surface coefficient of the 3rd surface and the4th surface) 3rd surface 4th surface κ −6.6181E−01 −1.6733E+02 A41.1149E−02 1.0501E−01 A6 2.4988E−03 −1.1650E−01 A8 1.8506E−05 1.0619E−01A10 2.9476E−04 −7.0978E−02 A12 6.5641E−05 2.7327E−02 A14 −4.2096E−05−4.3888E−03 A16 −3.6165E−06 A18 7.9919E−06 A20 −1.2231E−06 (Asphericalsurface coefficient, diffraction order, production wavelength, andoptical path difference function coefficient of the 2nd′ surface) The2nd′ surface AREA 14 AREA 15 (0 ≦ h ≦ 0.65) (0.65 ≦ h) κ 1.2071E+021.2071E+02 A4 1.7933E−03 1.7933E−03 A6 4.7511E−04 4.7511E−04 A8 0 0 A100 0 n2/n3 0/−1 — λB 785 nm — B2 −2.4556E−02 0 B4 7.1633E−04 0 B6 0 0 B80 0 B10 0 0

By the action of the superposition type diffractive structure HOE5formed in the tenth optical function area AREA 10, when themagnification m1 to the wavelength λ1 and the magnification m2 to thewavelength λ2 are made different from each other, the sphericalaberration due to the difference of the thickness between protectivelayers of the high density optical disk HD and DVD, is corrected.

Further, by the action of the diffractive structure DOE5 formed in the12th optical function area AREA 12 and the diffractive structure DOE6formed in the 13th optical function area AREA 13, the chromaticaberration in the blue violet area and the spherical aberrationfollowing the environmental temperature change are corrected.

When the wavelength change amount of the blue violet semiconductor laserLD1 by the mode-hopping, is assumed as +1 nm, to the change amount 151mλ RMS of the defocus component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 32 mλ RMS, and it can be seen that thechange of defocus component by the mode-hopping is finely corrected.

Further, in the case where the environmental temperature rises by 30°C., when the oscillation wavelength of the blue violet semiconductorlaser LD1 is 409.5 nm, the refractive index of the aberration correctingelement at the time, is 1.52079, and the refractive index of the lightconverging element L2 is 1.55671, to the change amount 116 mλ RDS of thespherical aberration component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 45 mλ RMS, and it can be seen that thespherical aberration change following the environmental temperaturechange, is finely corrected.

Further, in Table 17, numeric value data when the optical element of thepresent Example is combined with the coupling lens CUL as the divergentangle conversion element, is also shown.

The coupling lens CUL is an optical element for the purpose in which, byusing the action of the superposition type diffractive structure HOE6formed in the 14th optical function area AREA 14, the divergent anglesof the laser light flux of wavelength λ2 projected from the first lightemitting point EP1 and the laser light flux of the wavelength λ3projected from the second light emitting point EP2 are respectivelyconverted into divergent angles corresponding to the magnification m2 tothe wavelength λ2 of the objective optical system OBJ and themagnification m3 to the wavelength λ3, and they are projected.

Example 4

An optical element of Example 4 is an optimum optical element as theobjective optical system OBJ of the second optical pickup device asshown in FIG. 3, and the fifth optical pickup device PU5 as shown inFIG. 14, and its specific numeric data is shown in Table 18.

TABLE 18 (Example 4) (Optical specification of the optical element) HD:NA1 = 0.85, f1 = 2.200 mm, λ1 = 408 nm, m1 = 0, t1 = 0.0875 mm DVD: NA2= 0.67, f2 = 2.309 mm, λ2 = 658 nm, m2 = 0, t2 = 0.6 mm CD: NA3 =0.51,f3 = 2.281 mm, λ3 =785 nm, m3 = −1/8.000, t3 = 1.2 mm (Paraxial data)Surface d1 d2 d3 No. r(mm) mm mm (mm) Nλ1 Nλ2 Nλ3 vd OBJ ∞ ∞ 19.387 STO0.050 0.050 0.050 1 (lower 0.900 0.900 0.900 1.52424 1.50643 1.5049756.5 table) 2 (lower 0.050 0.050 0.050 table) 3 1.445 2.510 2.510 2.5101.55965 1.54062 1.53724 56.3 4 −4.540 0.679 0.477 0.330 5 ∞ 0.0875 0.6001.200 1.62110 1.57975 1.57326 30.0 6 ∞ (Paraxial radius of curvature ofthe 1st surface and 2nd surface, aspherical surface coefficient,diffraction order, production wavelength, optical path differencefunction coefficient) The 1st surface The 2nd surface AREA6 AREA7 AREA8AREA9 (0 ≦ h≦ 1.535) (1.535 ≦ h) (0 ≦ h ≦ 1.53) (1.53 ≦ h) r ∞ 231.761−117.433 −167.005 κ 0 0 0 9.6672E+01 A4 0 −1.2634E−04 −2.3039E−031.0847E−03 A6 0 −1.4443E−03 3.1515E−03 −2.2698E−04 A8 0 6.3328E−04−2.1791E−04 4.0064E−04 A10 0 −6.8934E−05 −5.9061E−05 −1.3815E−05n1/n2/n3 0/+1/0 — +2/+1/+1 +2/+1/+1 λB 658 nm — 390 nm 408 nm B2−4.7000E−03 0 −5.3000E−03 −5.2595E−03 B4 −5.5308E−04 0 5.6232E−04−3.8500E−04 B6 −2.5919E−04 0 −7.7644E−04 −2.8980E−04 B8 −2.0155E−05 05.1093E−05 5.6214E−05 B10 −2.0712E−07 0 1.4877E−05 −1.4307E−05(aspherical surface coefficient of the 3rd surface and the 4th surface)3rd surface 4th surface κ −6.6181E−01 −1.6733E+02 A4 1.1149E−021.0501E−01 A6 2.4988E−03 −1.1650E−01 A8 1.8506E−05 1.0619E−01 A102.9476E−04 −7.0978E−02 A12 6.5641E−05 2.7327E−02 A14 −4.2096E−05−4.3888E−03 A16 −3.6165E−06 A18 7.9919E−06 A20 −1.2231E−06

By the action of the superposition type diffractive structure HOE4(HOE8) formed in the sixth (18th) optical function area AREA 6 (AREA18), while the magnification m1 to the wavelength λ1 and themagnification m2 to the wavelength λ2 are made almost coincident witheach other, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected.

As a method by which, by the action of the superposition typediffractive structure, the spherical aberration due to the difference ofthe thickness between protective layers of the high density optical diskHD and DVD, is corrected, there are a method by which an undercorrection spherical aberration is added to the light flux of wavelengthλ2, and a method by which the paraxial diffraction power to the lightflux of wavelength λ2 is set to negative, however, in the former, thereis a problem in which the coma generation of the light flux ofwavelength λ2 due to the optical axis shift of the aberration correctingelement L1 and the light converging element L2 is large, and in thelatter, there is a problem in which, when the off-axis light flux ofwavelength λ2 enters, the coma generation is large.

In the superposition type diffractive structure HOE4 (HOE8) in thepresent Example, when both are combined with each other, the sphericalaberration due to the difference of the thickness between protectivelayers of the high density optical disk HD and DVD, is corrected, and inthe case where the paraxial diffraction power to the light flux ofwavelength λ2 is determined, a case which is made so that, while thecoma generation due to the optical axis shifting of the aberrationcorrecting element L1 and the light converging element L2 is softened,the off-axis characteristic to the light flux of wavelength λ2 is nottoo deteriorated, is minded.

Further, the optical path difference function of the superposition typediffractive structure HOE4 (HOE8) has an inflection point in NA2=0.67,and before and after the inflection point, the inclination of thetangential line is switched from positive to negative. This correspondsto that the inclination direction (numeral 14 in FIG. 3) of thering-shaped zone of the superposition type diffractive structure HOE4(HOE8) is reversed at the midway, and when the optical path differencefunction is made so as to have the inflection point in this manner, thewidth (Λ4 in FIG. 3) of the ring-shaped zone can be secured large. Inthe present Example, the minimum value of the width of the ring-shapedzone is 70 μm.

Further, by the action of the superposition type diffractive structureHOE3 (HOE8) formed in the eighth (the 20th) optical function area AREA 8(AREA 20) and the superposition type diffractive structure HOE4 (HOE9)formed in the ninth (the 21st) optical function area AREA 9 (AREA 21),the chromatic aberration in the blue violet area and the sphericalaberration change following the environmental temperature change arecorrected.

When the wavelength change amount of the blue violet semiconductor laserby the mode-hopping is assumed as +1 nm, to the change amount 151 mλ RMSof the defocus component in only the light converging element L2, whenthe light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 32 mλ RMS, and it can be seen that thechange of defocus component by the mode-hopping is finely corrected.

Further, in the case where the environmental temperature rises by 30°C., when the oscillation wavelength of the blue violet semiconductorlaser is 409.5 nm, the refractive index of the aberration correctingelement L1 at the time, is 1.52079, and the refractive index of thelight converging element L2 is 1.55671, to the change amount 114 mλ RMSof the spherical aberration component in only the light convergingelement L2, when the light converging element L2 is combined with theaberration correcting element L1, it becomes 46 mλ RMS, and it can beseen that the spherical aberration change following the environmentaltemperature change, is finely corrected.

Example 5

An optical element of Example 5 is an optimum optical element as anobjective optical system OBJ of the second optical pickup device PU2 asshown in FIG. 3, and the fifth optical pickup device PU5 as shown inFIG. 14, and its specific numerical value data will be shown in Table19.

TABLE 19 (Example 5) (Optical specification) ND: NA1 = 0.85, f1 = 2.200mm, λ1 = 408 nm, m1 =0, t1 =0.0875 mm DVD: NA2 = 0.67, f2 = 2.303 mm, λ2= 658 nm, m2 = 0, t2 = 0.6 mm CD: NA3 = 0.51, f3 = 2.272 mm, λ3 = 785nm, m3 = −1/7.062, t3 = 1.2 mm (Paraxial data) Surface d1 d2 d3 No.r(mm) (mm) (mm) (mm) Nλ1 Nλ2 Nλ3 vd OBJ ∞ ∞ 16.998 STO 0.050 0.050 0.0501 (lower 0.900 0.900 0.900 1.52424 1.50643 1.50497 56.5 table) 2 (lower0.050 0.050 0.050 table) 3 1.547 2.510 2.510 2.510 1.62225 1.603061.59924 61.2 4 −3.805 0.648 0.457 0.329 5 ∞ 0.0875 0.600 1.200 1.621101.57975 1.57326 30.0 6 ∞ (Paraxial radius of curvature of the 1stsurface and 2nd surface, aspherical surface coefficient, diffractionorder, production wavelength, optical path difference functioncoefficient) The 1st surface The 2nd surface (AREA6 AREA7 AREA8 AREA9 (0≦ h ≦ 1.55) (1.55 ≦ h) (0 ≦ h ≦ 1.53) (1.53 ≦ h) r ∞ 173.175 22.78420.692 κ 0 0 −1.6342E+02 4.9171E+01 A4 0 −2.2422E−03 1.7644E−033.0880E−04 A6 0 1.4856E−04 2.6776E−04 2.3114E−04 A8 0 2.0769E−044.7721E−04 1.4576E−04 A10 0 −3.7154E−05 −1.3338E−04 5.6460E−06 n1/n2/n30/+1/0 — +2/+1/+1 +3/+2/+2 λB 658 nm — 390 nm 408 nm B2 6.5000E−03 0−5.5000E−03 −3.7674E−03 B4 −7.2989E−04 0 −7.6775E−06 −2.6456E−04 B6−1.7631E−05 0 −1.3428E−04 −4.9605E−05 B8 −7.1954E−05 0 −1.0951E−041.6919E−05 B10 4.7865E−06 0 3.2640E−05 −7.9084E−06 (Aspherical surfacecoefficient of the 3rd surface and the 4th surface) 3rd surface 4thsurface κ −6.5500E−01 −1.1767E+02 A4 8.1711E−03 9.0672E−02 A6−4.6002E−04 −9.6820E−02 A8 2.3310E−03 7.6345E−02 A10 −1.3988E−03−4.9000E−02 A12 2.7074E−04 1.8605E−02 A14 2.2973E−04 −2.9535E−03 A16−1.6181E−04 A18 4.0853E−05 A20 −3.8604E−06

By the action of the superposition type diffractive structure HOE4(HOE8) formed in the sixth (18th) optical function area AREA 6 (AREA18), while the magnification m1 to the wavelength λ1 and themagnification m2 to the wavelength λ2 are made almost coincident witheach other, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected.

In the optical element of the present Example, in the same manner as theoptical element of Example 4, when a method by which the undercorrection spherical aberration is added to the light flux of wavelengthλ2, and a method by which the paraxial diffraction power to the lightflux of wavelength λ2 is set to negative, are combined, the sphericalaberration due to the difference of the thickness between protectivelayers of the high density optical disk HD and DVD, is corrected, andthe minimum value of the width of ring-shaped zone is 81 μm.

Further, by the action of the diffractive structure DOE3 (DOE8) formedin the eighth (20th) optical function area AREA 8 (AREA 20), and thediffractive structure DOE4 (DOE9) formed in the ninth (21st) opticalfunction area AREA 9 (AREA 21), the chromatic aberration in the blueviolet area and the spherical aberration change following the incidentwavelength change are corrected.

When the wavelength change amount of the blue violet semiconductor laserby the mode-hopping, is assumed as +1 nm, to the change amount 138 mλRMS of the defocus component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 18 mλ RMS, and it can be seen that thechange of defocus component by the mode-hopping is finely corrected.

Further, when the wavelength dispersion by the production error of theblue violet semiconductor laser is assumed as +10 nm, to the changeamount 54 mλ RMS of the spherical aberration component in only the lightconverging element L2, when the light converging element L2 is combinedwith the aberration correcting element L1, it becomes 4 mλ RMS, and itcan be seen that the change of spherical aberration following theincident wavelength change is finely corrected.

In the optical element of Example 2, the sectional view of thesuperposition type diffractive structure HOE4 formed in the sixthoptical function area AREA 6 is shown in FIG. 16, and in the opticalelement of Example 4, the sectional view of the superposition typediffractive structure HOE8 formed in the 18th optical function area AREA18 is shown in FIG. 17. In views, the horizontal axis indicates theheight h (mm) from the optical axis, and the vertical axis indicates theheight D (mm) in the direction perpendicular to the optical axis of thesuperposition type diffractive structure HOE4 (HOE8).

Example 6

An optical element of Example 6 is an optimum optical element as anobjective optical system OBJ of the eighth optical pickup device PU8 asshown in FIG. 20, and its specific numerical value data will be shown inTable 20. Further, the optical path view is shown in FIG. 23.

TABLE 20 (Example 6) (Optical specification) HD: NA1 = 0.85, f1 = 1.762mm, λ1 = 407 nm, m1 = 0, t1 = 0.1 mm DVD: NA2 = 0.65, f2 = 1.839 mm, λ2= 660 nm, m2 = 0, t2 = 0.6 mm (Paraxial data) Surface d1 d2 No. r(mm)(mm) (mm) Nλ1 Nλ2 vd OBJ ∞ ∞ STO 0.0500 0.0500 1 (lower 0.8000 0.80001.52439 1.50635 56.5 table) 2 (lower 0.0500 0.0500 table) 3 1.15781.9400 1.9400 1.55981 1.54055 56.3 4 −4.3607 0.5503 0.3187 5 ∞ 0.10000.6000 1.62000 1.58000 30.0 6 ∞ (Paraxial radius of curvature of the 1stsurface and 2nd surface, aspherical surface coefficient, diffractionorder, production wavelength, optical path difference functioncoefficient) The 1st surface AREA30 AREA31 The 2nd (0 ≦ h ≦ 1.19) (1.19≦ h) surface r ∞ −266.6972 30.0787 κ 0.0000E+00 0.0000E+00 −1.3500E+02A4 0.0000E+00 4.1672E−03 3.1459E−03 A6 0.0000E+00 −3.2275E−03 1.7821E−03A8 0.0000E+00 9.6415E−04 −4.7596E−04 A10 0.0000E+00 −7.1921E−053.5034E−04 n1/n2 0/+1 — +5/+3 λB 660 nm — 407 nm B2 6.0700E−030.0000E+00 −2.3000E−03 B4 −1.7226E−03 0.0000E+00 −4.3408E−04 B6−4.9632E−04 0.0000E+00 −1.0693E−04 B8 2.8654E−05 0.0000E+00 −5.8847E−06B10 −9.6694E−05 0.0000E+00 −2.2751E−05 (Aspherical surface coefficientof the 3rd surface and the 4th surface 3rd surface 4th surface κ−6.6194E−01 −2.0957E+02 A4 2.3605E−01 1.8576E−01 A6 7.3281E−02−3.1119E−01 A8 1.1210E−03 4.5733E−01 A10 2.0127E−03 −4.9600E−01 A126.6045E−04 3.0165E−01 A14 −8.1167E−04 −7.4912E−02 A16 −2.3825E−050.0000E+00 A18 3.8272E−04 0.0000E+00 A20 −1.0160E−04 0.0000E+00

By the action of the superposition type diffractive structure HOE12formed in the 30th optical function area AREA 30, the sphericalaberration due to the difference of thickness between the protectivelayers of the high density optical disk and DVD, is corrected and theaperture limit when DVD is used, is automatically conducted by theaberration correcting element L1.

In the optical element of the present Example, when a method by which,when signs of the second degree optical path difference functioncoefficient B2 and the 4th degree optical path difference functioncoefficient B4 of the superposition type diffractive structure HOE12 aremade different, the under correction spherical aberration is added tothe light flux of wavelength λ2, and a method by which the paraxialdiffraction power to the light flux of wavelength λ2 is set to negative,are combined, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected. The minimum value of the width of the ring-shapedzone of the superposition type diffractive structure is 117.4 μm, andbecause the sufficient width of the ring-shaped zone is obtained, themetallic mold processing is easy.

Further, by the action of the diffractive structure DOE13 formed on theoptical function surface S2 on the optical disk side of the aberrationcorrecting element L1, the axial chromatic aberration in the blue violetarea and the spherical aberration change following the environmentaltemperature change are corrected.

When the wavelength change amount of the blue violet semiconductor laserby the mode-hopping, is assumed as +1 nm, to the change amount 119 mλRMS of the defocus component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 35 mλ RMS, and it can be seen that thechange of defocus component by the mode-hopping is finely corrected.

Further, in the case where the environmental temperature rises by 30°C., when the oscillation wavelength of the blue violet semiconductorlaser is 408.5 nm, the refractive index of the aberration correctingelement L1 at the time, is 1.52094, and the refractive index of thelight converging element L2 is 1.55687, to the change amount 89 mλ RMSof the spherical aberration component in only the light convergingelement L2, when the light converging element L2 is combined with theaberration correcting element L1, it becomes 28 mλ RMS, and it can beseen that the spherical aberration change following the environmentaltemperature change, is finely corrected.

Example 7

An optical element of Example 7 is an optimum optical element as anobjective optical system OBJ of the ninth optical pickup device PU9 asshown in FIG. 21, and its specific numerical value data will be shown inTable 21. Further, the optical path view is shown in FIG. 24.

TABLE 21 (Example 7) (Optical specification) HD: NA1 = 0.85, f1 = 1.765mm, λ1 = 405 nm, m1 = 0, t1 = 0.1 mm DVD: NA2 = 0.65, f2 = 1.826 mm, λ2= 650 nm, m2 = 0, t2 = 0.6 mm (Paraxial data) Surface d1 d2 No. r(mm)(mm) (mm) Nλ1 Nλ2 vd OBJ ∞ ∞ STO 0.0500 0.0500 1 (lower 1.0000 1.00001.52469 1.50668 56.5 table) 2 (lower 0.2000 0.2000 table) 3 1.23722.1400 2.1400 1.62272 1.60337 61.2 4 −3.3048 0.5319 0.3001 5 ∞ 0.10000.6000 1.62000 1.58000 30.0 6 ∞ (Paraxial radius of curvature of the 1stsurface and 2nd surface, aspherical surface coefficient, diffractionorder, production wavelength, optical path difference functioncoefficient) The 1st surface AREA32 AREA33 The 2nd (0 ≦ h ≦ 1.19) (1.19≦ h) surface r ∞ ∞ 19.4381 κ 0.0000E+00 0.0000E+00 5.2930E+01 A40.0000E+00 0.0000E+00 2.1118E−03 A6 0.0000E+00 0.0000E+00 6.7171E−04 A80.0000E+00 0.0000E+00 3.6437E−05 A10 0.0000E+00 0.0000E+00 1.4947E−04n1/n2 0/+1 — +5/+3 λB 650 nm — 405 nm B2 7.1500E−03 0.0000E+00−2.7000E−03 B4 −2.1522E−03 0.0000E+00 −3.2200E−04 B6 2.7312E−040.0000E+00 −7.3772E−05 B8 −6.4452E−04 0.0000E+00 −5.8735E−06 B101.0262E−04 0.0000E+00 −1.5541E−05 (Aspherical surface coefficient of the3rd surface and the 4th surface) 3rd surface 4th surface κ −6.5735E−01−1.1212E+02 A4 1.5546E−02 1.5169E−01 A6 −1.0395E−03 −2.5481E−01 A81.0347E−02 3.5667E−01 A10 −9.7392E−03 −3.7802E−01 A12 2.9457E−032.1856E−01 A14 3.9500E−03 −5.1014E−02 A16 −4.3906E−03 0.0000E+00 A181.7571E−03 0.0000E+00 A20 −2.6284E−03 0.0000E+00

By the action of the superposition type diffractive structure HOE13formed in the 32nd optical function area AREA 32, the sphericalaberration due to the difference of thickness between the protectivelayers of the high density optical disk and DVD, is corrected and theaperture limit when DVD is used, is automatically conducted by theaberration correcting element L1.

In the optical element of the present Example, when a method by which,when signs of the second degree optical path difference functioncoefficient B2 and the 4th degree optical path difference functioncoefficient B4 of the superposition type diffractive structure HOE13 aremade different, the under correction spherical aberration is added tothe light flux of wavelength λ2, and a method by which the paraxialdiffraction power to the light flux of wavelength λ2 is set to negative,are combined, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected. The minimum value of the width of the ring-shapedzone of the superposition type diffractive structure is 93.8 μm, andbecause the sufficient width of the ring-shaped zone is obtained, themetallic mold processing is easy.

Further, by the action of the diffractive structure DOE13 formed on theoptical function surface S2 on the optical disk side of the aberrationcorrecting element L1, the axial chromatic aberration in the blue violetarea and the spherical aberration change are corrected.

When the wavelength change amount of the blue violet semiconductor laserby the mode-hopping, is assumed as +1 nm, to the change amount 114 mλRMS of the defocus component in only the light converging element L2,when the light converging element L2 is combined with the aberrationcorrecting element L1, it becomes 23 mλ RMS, and it can be seen that thechange of defocus component by the mode-hopping is finely corrected.

Further, in the case where the wavelength dispersion by the productionerror of the blue violet semiconductor laser is assumed as +10 nm, tothe change amount 47 mλ RMS of the spherical aberration component inonly the light converging element L2, when the light converging elementL2 is combined with the aberration correcting element L1, it becomes 4mλ RMS, and it can be seen that the spherical aberration changefollowing the incident wavelength change, is finely corrected.

Example 8

An optical element of Example 8 is an optimum optical element as anobjective optical system OBJ of the tenth optical device PU10 as shownin FIG. 22, and its specific numerical value data will be shown in Table22. Further, the optical path view is shown in FIG. 25.

TABLE 22 (Example 8) (Optical specification) HD: NA1 = 0.85, f1 = 1.802mm, λ1 = 407 nm, m1 = 0, t1 = 0.0875 mm DVD: NA2 = 0.65, f2 = 1.888 mm,λ2 = 660 nm, m2 = 0, t2 = 0.6 mm (Paraxial data) Surface No. r (mm) d1(mm) d2 (mm) Nλ1 Nλ2 νd OBJ ∞ ∞ STO 0.0500 0.0500 1 10.7695 0.80000.8000 1.52439 1.50639 56.5 (lower table) 2 (lower 0.0500 0.0500 table)3 1.1589 1.9400 1.9400 1.55981 1.54055 61.2 4 −4.9861 0.5361 0.2719 5 ∞0.0875 0.6000 1.62000 1.58000 30.0 6 ∞ (Paraxial radius of curvature ofthe 2nd surface, aspherical surface coefficient, diffraction order,production wavelength, optical path difference function coefficient) The2nd surface AREA 34 AREA 35 (0 ≦ h ≦ 1.19) (1.19 ≦ h) r ∞ ∞ κ 0.0000E+000.0000E+00 A4 0.0000E+00 0.0000E+00 A6 0.0000E+00 0.0000E+00 A80.0000E+00 0.0000E+00 A10 0.0000E+00 0.0000E+00 n1/n2 0/+1 — λB 660 nm —B2 5.0000E−03 0.0000E+00 B4 −2.0707E−03 0.0000E+00 B6 −7.1074E−050.0000E+00 B8 −3.5082E−04 0.0000E+00 B10 −1.9639E−06 0.0000E+00(Aspherical surface coefficient of the 1st surface, 3rd surface and 4thsurface) 1st surface 3rd surface 4th surface κ 2.5831E−01 −6.5345E−01−3.5746E+02 A4 −8.3565E−05 2.4534E−02 1.8708E−01 A6 1.3321E−067.3164E−03 −2.9678E−01 A8 0.0000E+00 2.1062E−03 4.3464E−01 A100.0000E+00 1.2314E−03 −5.1105E−01 A12 0.0000E+00 8.8703E−04 3.4582E−01A14 0.0000E+00 −5.3424E−04 −9.5672E−02 A16 0.0000E+00 −7.5068E−050.0000E+00 A18 0.0000E+00 2.9623E−04 0.0000E+00 A20 0.0000E+00−6.5778E−05 0.0000E+00 (Optical path difference grant structure of the1st surface) i h_(is) (mm) h_(iL) (mm) m_(i1d) (mm) m_(i1) m_(i2) 00.0000 0.5800 0.000000 0 0 1 0.5800 0.8600 0.003881 −5 −3 2 0.86001.3800 0.007761 −10 −6 3 1.3800 1.4500 0.003881 −5 −3 4 1.4500 1.50000.000000 0 0 5 1.5000 1.5300 −0.003881 5 3 6 1.5300 1.5600 −0.007761 106

By the action of the superposition type diffractive structure HOE14formed in the 34th optical function area AREA 34, the sphericalaberration due to the difference of thickness between the protectivelayers of the high density optical disk and DVD, is corrected and theaperture limit when DVD is used, is automatically conducted by theaberration correcting element L1.

In the optical element of the present Example, when a method by which,when signs of the second degree optical path difference functioncoefficient B2 and the 4th degree optical path difference functioncoefficient B4 of the superposition type diffractive structure HOE14 aremade different, the under correction spherical aberration is added tothe light flux of wavelength λ2, and a method by which the paraxialdiffraction power to the light flux of wavelength λ2 is set to negative,are combined, the spherical aberration due to the difference of thethickness between protective layers of the high density optical disk HDand DVD, is corrected. The minimum value of the width of the ring-shapedzone of the superposition type diffractive structure HOE14 is 66.3 μm,and because the sufficient width of the ring-shaped zone is obtained,the metallic mold processing is easy.

Further, by the action of the optical path difference grant structureNPS formed on the optical function surface S1 on the semiconductor laserside of the aberration correcting element L1, the spherical aberrationchange following the environmental temperature change in the blue violetarea are corrected.

Further, in the case where the environmental temperature rises by 30°C., when the oscillation wavelength of the blue violet semiconductorlaser is 408.5 nm, the refractive index of the aberration correctingelement L1 at the time, is 1.52094, and the refractive index of thelight converging element L2 is 1.55687, to the change amount 81 mλ RMSof the spherical aberration component in only the light convergingelement L2, when the light converging element L2 is combined with theaberration correcting element L1, it becomes 15 mλ RMS, and it can beseen that the spherical aberration change following the environmentaltemperature change, is finely corrected.

Hereupon, in (the optical path difference grant structure of the firstsurface) of Table 22-2, i shows the number of the central area and eachring-shaped zone, and the first ring shaped zone adjoining the outsideof the central area is i=1, and the second ring-shaped zone adjoiningthe outside of the first ring-shaped zone is i=2. A sign his shows theheight of start point of the central area and each ring-shaped zone, andh_(iL) shows the height of end point of the central area and eachring-shaped zone. Further, mild shows the shift amount in the opticalaxis direction of each ring-shaped zone to the central area. Forexample, the second ring-shaped zone (i=2) shifts toward the opticaldisk side by 7.761 μm to the central area (i=0), and the sixthring-shaped zone (I=6) shifts toward the laser light source side by7.761 μm to the central area (i=0). Further, a sign mild is a value inwhich the optical path length difference of each ring-shaped zone to thecentral area is expressed by making the wavelength λ1 (=407 nm) as aunit, and m_(i2) is a value in which the optical path length differenceof each ring-shaped zone to the central area is expressed by making thewavelength λ2 (=660 nm) as a unit. For example, in the secondring-shaped zone, the optical path length is shorter by 10×λ1(6×λ2) tothe central area, and the sixth ring-shaped zone, the optical pathlength is length is longer by 10×λ1 (6×λ2) to the central area.

Example 9

The optical system in Example 9 is an optical system composed of anexpander lens that is composed of a negative lens and a positive lensboth representing a plastic lens and of an objective optical systemcomposed of an aberration correcting element and a light-convergingelement both representing a plastic lens, and it is most appropriate asan optical system for the 12^(th) optical pickup device PU12. Table 23shows its specific numerical values data.

TABLE 23 (Example 9) (Optical specifications) f1 = 2.200, NA1 = 0.85, λ1= 408 nm, d2 = 3.0000, d8 = 0.7190, d9(t1) = 0.0875 f2 = 2.278, NA2 =0.65, λ2 = 658 nm, d2 = 3.1800, d8 = 0.4770, d9(t2) = 0.6 f3 = 2.275,NA3 = 0.45, λ3 = 785 nm, d2 = 0.2000, d8 = 0.4290, d9(t3) = 1.2(Paraxial data) Surface No. r (mm) d (mm) Nλ1 Nλ2 Nλ3 νd Remarks OBJ ∞Light-emitting point 1 −1.0991 0.8000 1.5242 1.5064 1.5050 56.5 Expanderlens 2 1.9354 d2 3 ∞ 1.5000 1.5242 1.5064 1.5050 56.5 4 −2.8923 15.000STO 0.5000 Diaphragm 5 ∞ 1.0000 1.5242 1.5064 1.5050 56.5 Objectiveoptical system 6 ∞ 0.1000 7 1.4492 2.6200 1.5596 1.5406 1.5372 56.3 8−2.8750 d8 9 ∞ d9 1.6211 1.5798 1.5733 30.0 Protective layer 10  ∞(Aspherical surface coefficient) First Second Fourth Seventh Eighthsurface surface surface surface surface κ −0.10191E+01 0.11413E+01−0.42828E+00 −0.65249E+00 −0.43576E+02 A4 −0.54020E−01 −0.59836E−01−0.29680E−04 0.77549E−02 0.97256E−01 A6 0.00000E+00 0.00000E+000.00000E+00 0.29588E−03 −0.10617E+00 A8 0.00000E+00 0.00000E+000.00000E+00 0.19226E−02 0.81812E−01 A10 0.00000E+00 0.00000E+000.00000E+00 −0.12294E−02 −0.41190E−01 A12 0.00000E+00 0.00000E+000.00000E+00 0.29138E−03 0.11458E−01 A14 0.00000E+00 0.00000E+000.00000E+00 0.21569E−03 −0.13277E−02 A16 0.00000E+00 0.00000E+000.00000E+00 −0.16850E−03 0.00000E+00 A18 0.00000E+00 0.00000E+000.00000E+00 0.44948E−04 0.00000E+00 A20 0.00000E+00 0.00000E+000.00000E+00 −0.43471E−05 0.00000E+00 Optical path difference functioncoefficient Fifth surface n1/n2/n3 0/1/0 λB 658 nm B2 3.6500E−03 B4−1.0196E−03 B6 1.6630E−05 B8 −9.3691E−05 B10 9.0441E−06

The objective optical system is a HD/DVD compatible lens whereinspherical aberration caused by a difference of protective layerthickness between high density optical disc HD and DVD has beencorrected by actions of a superposed type diffractive structure formedon an optical surface (Fifth surface in Table 23) closer to the lightsource on the aberration correcting element. Incidentally, thelight-converging element is a lens optimized in terms of sphericalaberration correction for high density optical disc HD.

Further, spherical aberration caused by a protective layer thicknessdifference between high density optical disc HD and CD is corrected bychanging a magnification of an objective optical system by moving anegative lens of an expander lens in the optical axis direction.

When a wavelength of an incident light flux is changed, a degree ofdivergence of a light flux emerging from the expander lens is changed byan influence of chromatic aberration. When conductingrecording/reproducing for DVD, therefore, a negative lens is moved tomake a distance between the negative lens and a positive lens to begreater than that in the case of high density optical disc HD, so thatthe second light flux emerging from the expander lens may become aparallel light flux.

Incidentally, diffraction efficiency of 0-order diffracted light ray(transmitted light) of the first light flux generated by the superposedtype diffractive structure is 100%, diffraction efficiency of firstorder diffracted light ray of the second light flux is 87% anddiffraction efficiency of 0-order diffracted light ray (transmittedlight) for the third light flux is 100%, and high diffractionefficiencies are obtained for all light fluxes.

Example 10

The optical system in Example 10 is an optical system composed of anexpander lens which is a plastic lens and of an objective optical systemwhich is a plastic lens, and it is most appropriate as an optical systemfor 12^(th) optical pickup device PU12. Further, the objective opticalsystem in the present example is optimum as an objective optical systemfor 11^(th) optical pickup device PU11. Table 24 shows its specificnumerical values data.

TABLE 24 (Example 10) (Optical specifications) f1 = 2.200, NA1 = 0.85,λ1 = 408 nm, d0 = 11.1247, d2 = 15.0000, d4 = 0.6988, d5(t1) = 0.0875 f2= 2.264, NA2 = 0.60, λ2 = 658 nm, d0 = 11.5247, d2 = 14.6000, d4 =0.4280, d5(t2) = 0.6 f3 = 2.276, NA3 = 0.45, λ3 = 785 nm, d0 = 9.1747,d2 = 16.9500, d4 = 0.1325, d5(t3) = 1.2 (Paraxial data) Sur- face No. r(mm) d (mm) Nλ1 Nλ2 Nλ3 νd Remarks OBJ d0 Light- emitting point 161.0791 1.5000 1.5242 1.5064 1.5050 56.5 Collimator 2 −6.9631 d2 lensSTO 0.5000 Dia- phragm 3 1.4293 2.6200 1.5596 1.5406 1.5372 56.3Objective 4 −3.0401 d4 optical system 5 ∞ d5 1.6211 1.5798 1.5733 30.0Protective 6 ∞ layer (Aspherical surface coefficient) First Second ThirdFourth surface surface surface surface κ −0.67089E+02 −0.65737E+00−6.7004E−01 −0.54707E+02 A4 0.00000E+00 0.00000E+00 6.2259E−030.10933E+00 A6 0.00000E+00 0.00000E+00 5.2878E−05 −0.11038E+00 A80.00000E+00 0.00000E+00 1.8134E−03 0.79680E−01 A10 0.00000E+000.00000E+00 −1.2562E−03 −0.40854E−01 A12 0.00000E+00 0.00000E+002.9205E−04 0.12151E−01 A14 0.00000E+00 0.00000E+00 2.1716E−04−0.15470E−02 A16 0.00000E+00 0.00000E+00 −1.6878E−04 0.00000E+00 A180.00000E+00 0.00000E+00 4.4777E−05 0.00000E+00 A20 0.00000E+000.00000E+00 −4.3471E−06 0.00000E+00 Optical path difference functioncoefficient Third surface n1/n2/n3 1/1/1 λB 480 nm B2 0.00000E+00 B4−2.0425E−03 B6 −2.0631E−04 B8 −8.8830E−05 B10 −1.0296E−05

The objective optical system is a HD/DVD compatible lens whereinspherical aberration caused by a difference of protective layerthickness between high density optical disc HD and DVD has beencorrected by actions of a diffractive structure formed on an opticalsurface (Third surface in Table 24) closer to a light source.

Further, spherical aberration caused by a protective layer thicknessdifference between high density optical disc HD and CD is corrected bymoving a collimator lens in the optical axis direction and thereby, bychanging a magnification of an objective optical system, and sphericalaberration caused by a protective layer thickness difference betweenhigh density optical disc HD and CD is reduced by utilizing primarydiffracted rays of light of the first-third light fluxes on thediffractive structure, which makes an amount of movement of thecollimator lens to be small, and improves tracking characteristics ofthe objective optical system.

Further, when a wavelength of an incident light flux is changed, adegree of divergence of a light flux emerging from the collimator lensis changed by an influence of chromatic aberration. When conductingrecording/reproducing for DVD, therefore, a collimator lens is moved tomake a distance between the collimator lens and an objective opticalsystem to be smaller than that in the case of high density optical discHD, so that the second light flux emerging from the collimator lens maybecome a parallel light flux.

Incidentally, diffraction efficiency of primary diffracted light ray ofthe first light flux generated by the diffractive structure is 88%,diffraction efficiency of primary diffracted light ray of the secondlight flux is 76% and diffraction efficiency of primary diffracted lightray of the third light flux is 50%, thus, by setting manufacturewavelength λB at 480 nm, high diffraction efficiencies are obtained forhigh density optical disc HD and DVD which are requested to have highspeed recording.

Example 11

The optical system in Example 11 is an optical system composed of anexpander lens which is composed of a negative lens and a protective lensboth representing a plastic lens and of an object optical system whichis composed of an aberration correcting element and a light-convergingelement both representing a plastic lens, and it is most appropriate asan optical system for 12^(th) optical pickup device PU12. Table 25 showsits specific numerical values data.

TABLE 25 (Example 11) (Optical specifications) f1 = 2.200, NA1 = 0.85,λ1 = 408 nm, d2 = 3.0000, d8 = 0.7185, d9(t1) = 0.0875 f2 = 2.276, NA2 =0.65, λ2 = 658 nm, d2 = 3.1400, d8 = 0.4835, d9(t2) = 0.6 f3 = 2.328,NA3 = 0.45, λ3 = 785 nm, d2 = 1.4900, d8 = 0.2633, d9(t3) = 1.2(Paraxial data) Surface No. r (mm) d (mm) Nλ1 Nλ2 Nλ3 νd Remarks OBJ ∞Light- emitting point 1 −3.9344 0.8000 1.5242 1.5064 1.5050 56.5Expander 2 5.1986 d2 lens 3 30.1721 1.5000 1.5242 1.5064 1.5050 56.5 4−4.9932 15.000 STO 0.5000 Diaphragm 5 ∞ 1.0000 1.5242 1.5064 1.5050 56.5Objective 6 6.55303 0.1000 optical 7 1.4492 2.6200 1.5596 1.5406 1.537256.3 system 8 −2.8750 d8 9 ∞ d9 1.6211 1.5798 1.5733 30.0 Protective 10∞ layer (Aspheric surface coefficient) First Second Third Fourth SixthSeventh Eighth surface surface surface surface surface surface surface κ−0.68486E+00 −0.51627E+00 −0.53651E+02 −0.12346E+00 0.00000E+00−0.65249E+00 −0.43576E+02 A4 0.00000E+00 0.00000E+00 0.00000E+000.00000E+00 −1.45920E−02 0.77549E−02 0.97256E−01 A6 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00 2.32980E−05 0.29588E−03 −0.10617E+00A8 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 −5.48820E−060.19226E−02 0.81812E−01 A10 0.00000E+00 0.00000E+00 0.00000E+000.00000E+00 2.68810E−07 −0.12294E−02 −0.41190E−01 A12 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.29138E−03 0.11458E−01A14 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+000.21569E−03 −0.13277E−02 A16 0.00000E+00 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 −0.16850E−03 0.00000E+00 A18 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.44948E−04 0.00000E+00A20 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00−0.43471E−05 0.00000E+00 (Optical path difference function coefficient)Fifth surface Sixth surface n1/n2/n3 0/1/0 5/3/2 λB 658 nm 408 nm B23.6500E−03 −8.0000E−03 B4 −9.6924E−04 1.4770E−03 B6 −5.2431E−050.0000E+00 B8 −5.7323E−05 0.0000E+00 B10 1.6570E−06 0.0000E+00

The objective optical system is a HD/DVD compatible lens whereinspherical aberration caused by a difference of protective layerthickness between high density optical disc HD and DVD has beencorrected by actions of a superposed type diffractive structure formedon an optical surface (Fifth surface in Table 25) closer to a lightsource on an aberration correcting element. Incidentally, thelight-converging element is a lens which is optimized in terms ofspherical aberration correction for high density optical disc HD.

Further, spherical aberration caused by a protective layer thicknessdifference between high density optical disc HD and CD is corrected bymoving a negative lens of an expander lens in the optical axis directionand thereby, by changing a magnification of an objective optical system,and spherical aberration caused by a protective layer thicknessdifference between high density optical disc HD and CD is reduced byutilizing 5^(th) order diffracted light ray of the first light flux,3^(rd) order diffracted light ray of the second light flux and 2^(nd)order diffracted light ray of the third light flux on the diffractivestructure formed on an optical surface (sixth surface in Table 25)closer to an optical disc on the aberration correcting element, whichmakes an amount of movement of the negative lens to be small, andimproves tracking characteristics of the objective optical system.

Further, when a wavelength of an incident light flux is changed, adegree of divergence of a light flux emerging from the expander lens ischanged by an influence of chromatic aberration. When conductingrecording/reproducing for DVD, therefore, a negative lens is moved tomake a distance between the negative lens and the positive lens to begreater than that in the case of high density optical disc HD, so thatthe second light flux emerging from the expander lens may become aparallel light flux.

Incidentally, diffraction efficiency of 0-order diffracted light ray(transmitted light) of the first light flux generated by the superposedtype diffractive structure is 100%, diffraction efficiency of firstorder diffracted light ray of the second light flux is 87% anddiffraction efficiency of 0-order diffracted light ray (transmittedlight) for the third light flux is 100%, while, diffraction efficiencyof 5^(th) order diffracted light ray of the first light flux generatedby the diffractive structure is 100%, diffraction efficiency of thirdorder diffracted light ray of the second light flux is 100% anddiffraction efficiency of 2^(nd) order diffraction light ray for thethird light flux is 41%. Thus, the diffraction efficiencies by the twodiffractive structure represent 100% for the first light flux, 87% forthe second light flux and 41% for the third light flux, which means thathigh diffraction efficiencies are obtained for high density optical discHD and for DVD both being requested to have high speed recording.

1. An optical system for use in an optical pickup apparatus in whichreproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first wavelength λ1emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising: a first optical surface having asuperposition type diffractive structure including a plurality ofring-shaped zones which are formed concentrically around an opticalaxis, wherein each ring-shaped zone is composed of a plurality ofstepped sections stepwise, and a second optical surface having adiffractive structure including a plurality of ring-shaped zones whichare formed concentrically around an optical axis, wherein each of theplurality of ring-shaped zones are divided by a stepped section togenerate a diffractive light ray of diffractive order whose absolutevalue is not small than 1 for the light flux.
 2. The optical system ofclaim 1, wherein the depth of the stepped section of the diffractivestructure satisfies the following formula (1):n1>n2 where n1 is a diffraction order of a diffracted ray having themaximum diffraction efficiency among diffracted rays generated when alight flux having the first light wavelength λ1 enters into thediffractive structure, and n2 is a diffraction order of a diffracted rayhaving the maximum diffraction efficiency among diffracted raysgenerated when a light flux having the second light wavelength λ2 entersinto the diffractive structure.
 3. The optical system of claim 2,wherein when the first wavelength λ1 (μm) and the second wavelength λ2(μm) satisfy the formulas (2) and (3) respectively,0.39<λ1<0.42  (2)0.63<λ2<0.68  (3), a combination of the diffraction orders n1 and n2 isany of (n1, n2)=(2, 1), (3, 2), (5, 3), (8, 5) and (10, 6).
 4. Theoptical system of claim 3, wherein an optical element having the secondoptical surface has a refractive index of 1.5 to 1.6 and is made of amaterial having Abbe constant of 50 to 60 for d-line, and the depth d1of the stepped section of a ring-shaped zone located closest to theoptical axis among the plurality of ring-shaped zones of the diffractivestructure satisfies any one of formulas (4) to (8):1. 2 μm<d1<1.7 μm  (4)2. 0 μm<d1<2.6 μm  (5)3. 4 μm<d1<4.1 μm  (6)5. 6 μm<d1<6.5 μm  (7)6. 9 μm<d1<8.1 μm  (8)
 5. The optical system of claim 4, wherein a crosssectional form of the diffractive structure including the optical axisis shaped stepwise.
 6. The optical system of claim 5, wherein theoptical system of the optical pickup apparatus consists of a singleoptical element and one optical surface of the optical element includesthe superposition type diffractive structure and the other opticalsurface includes the diffractive structure.
 7. The optical system ofclaim 6, wherein the superposition type diffractive structure does notsubstantially provide an optical path difference between neighboringstepped sections for the first wavelength λ1 and provide an optical pathdifference between neighboring stepped sections for the first wavelengthλ2.
 8. The optical system of claim 7, wherein the first wavelength λ1(μm) and the second wavelength λ2 (μm) satisfy the formulas (2) and (3)respectively,0.39<λ1<0.42  (2)0.63<λ2<0.68  (3).
 9. The optical system of claim 4, wherein a crosssectional form of the diffractive structure including the optical axisis shaped in saw-tooth.
 10. The optical system of claim 9, wherein theoptical system of the optical pickup apparatus consists of a singleoptical element and one optical surface of the optical element includesthe superposition type diffractive structure and the other opticalsurface includes the diffractive structure.
 11. The optical system ofclaim 10, wherein the superposition type diffractive structure does notsubstantially provide an optical path difference between neighboringstepped sections for the first wavelength λ1 and provide an optical pathdifference between neighboring stepped sections for the first wavelengthλ2.
 12. The optical system of claim 11, wherein the first wavelength λ1(μm) and the second wavelength λ2 (μm) satisfy the formulas (2) and (3)respectively,0.39<λ1<0.42  (2)0.63<λ2<0.68  (3).
 13. An objective optical system for use in an opticalpickup apparatus including the optical system described in claim 12, toconverge the first wavelength λ1 onto an information recording plane ofthe first optical information recording medium and to converge thesecond wavelength λ2 onto an information recording plane of the secondoptical information recording medium, wherein the diffractive structurehas a function to refrain a chromatic aberration caused by the objectiveoptical system due to wavelength fluctuation when the first wavelengthλ1 fluctuates within a range of ±10 nm.
 14. The objective optical systemof claim 13, wherein when the first wavelength λ1 fluctuates within arange of ±10 nm, the diffractive structure refrains a longitudinalchromatic aberration caused by the objective optical system.
 15. Theobjective optical system of claim 14, wherein when the first wavelengthλ1 fluctuates within a range of ±10 nm, the diffractive structurerefrains a change of a spherical aberration caused by the objectiveoptical system due to the wavelength fluctuation.
 16. The objectiveoptical system of claim 12, wherein the objective optical systemincludes a plastic lens having a positive power on paraxial and thediffractive structure has a function to refrain a change of a sphericalaberration caused due to a change of a refractive index of the plasticlens when environmental temperature changes.
 17. The objective opticalsystem of claim 16, wherein the objective optical system has awavelength dependency in a spherical aberration such that when the firstwavelength λ1 changes toward to a longer wavelength side, a sphericalaberration changes toward to be under-corrected and when the firstwavelength λ1 changes toward to a shorter wavelength side, a sphericalaberration changes toward to be over-corrected.
 18. The objectiveoptical system of claim 17, wherein objective optical system comprises acorrecting optical system and a light converging element to converge alight flux having a wavelength λ1 emitted from the correcting opticalsystem on an information recording plane of the first opticalinformation recording medium and to converge a light flux having awavelength λ2 emitted from the correcting optical system on aninformation recording plane of the second optical information recordingmedium.
 19. The objective optical system of claim 18, wherein thesuperposition type diffractive structure has a function to correct aspherical aberration caused due to a difference in thickness between aprotective substrate of the first optical information recording mediumand a protective substrate of the second optical information recordingmedium.
 20. The optical system of claim 1, wherein the superpositiontype diffractive structure does not substantially provide an opticalpath difference between neighboring stepped sections for the firstwavelength λ1 and provide an optical path difference between neighboringstepped sections for the first wavelength λ2.
 21. An objective opticalsystem for use in an optical pickup apparatus including the opticalsystem described in claim 1, to converge the first wavelength λ1 onto aninformation recording plane of the first optical information recordingmedium and to converge the second wavelength λ2 onto an informationrecording plane of the second optical information recording medium,wherein the diffractive structure has a function to refrain a chromaticaberration caused by the objective optical system due to wavelengthfluctuation when the first wavelength λ1 fluctuates within a range of±10 nm.
 22. The objective optical system of claim 21, wherein when thefirst wavelength λ1 fluctuates within a range of ±10 nm, the diffractivestructure refrains a longitudinal chromatic aberration caused by theobjective optical system.
 23. The objective optical system of claim 22,wherein when the first wavelength λ1 fluctuates within a range of ±10nm, the diffractive structure refrains a change of a sphericalaberration caused by the objective optical system due to the wavelengthfluctuation.
 24. An objective optical system for use in an opticalpickup apparatus including the optical system described in claim 1, toconverge the first wavelength λ1 onto an information recording plane ofthe first optical information recording medium and to converge thesecond wavelength λ2 onto an information recording plane of the secondoptical information recording medium, wherein the objective opticalsystem includes a plastic lens having a positive power on paraxial andthe diffractive structure has a function to refrain a change of aspherical aberration caused due to a change of a refractive index of theplastic lens when environmental temperature changes.
 25. The objectiveoptical system of claim 24, wherein the objective optical system has awavelength dependency in a spherical aberration such that when the firstwavelength λ1 changes toward to a longer wavelength side, a sphericalaberration changes toward to be under-corrected and when the firstwavelength λ1 changes toward to a shorter wavelength side, a sphericalaberration changes toward to be over-corrected.
 26. The objectiveoptical system of claim 25, wherein objective optical system comprises acorrecting optical system and a light converging element to converge alight flux having a wavelength λ1 emitted from the correcting opticalsystem on an information recording plane of the first opticalinformation recording medium and to converge a light flux having awavelength λ2 emitted from the correcting optical system on aninformation recording plane of the second optical information recordingmedium.
 27. The objective optical system of claim 26, wherein thesuperposition type diffractive structure has a function to correct aspherical aberration caused due to a difference in thickness between aprotective substrate of the first optical information recording mediumand a protective substrate of the second optical information recordingmedium. 28-51. (canceled)
 52. An optical system for use in an opticalpickup apparatus in which reproducing and/or recording information isconducted for a first optical information recording medium equipped witha protective layer having a thickness t1 by using a light flux having afirst wavelength λ1 emitted from a first light source and reproducingand/or recording information is conducted for a second opticalinformation recording medium equipped with a protective layer having athickness t2 (t2≧t1) by using a light flux having a second wavelength λ2(λ2>λ1) emitted from a second light source, comprising: a correctingoptical system; a light converging element to converge a light fluxhaving a wavelength λ1 emitted from the correcting optical system on aninformation recording plane of the first optical information recordingmedium and to converge a light flux having a wavelength λ2 emitted fromthe correcting optical system on an information recording plane of thesecond optical information recording medium; wherein an optical surfaceof the correcting optical system has a plurality of optical functionalzones, and a superposition type diffractive structure is formed withinone of the plurality of optical functional zones such that a pluralityof ring-shaped zones are formed concentrically around the optical axisand plural stepped sections shaped stepwise are formed within eachring-shaped zone.
 53. The optical system of claim 52, wherein a firstmagnification m in the case that reproducing and/or recordinginformation is conducted for a first optical information recordingmedium almost coincides with a second magnification m2 in the case thatreproducing and/or recording information is conducted for a secondoptical information recording medium.
 54. The optical system of claim53, wherein the optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources.55. The optical system of claim 53, wherein the optical system convergesa light flux having the first wavelength λ1 emitted from a light sourcemodule, in which the first and second light sources are packaged, on aninformation recording plane of the first optical information recordingmedium and converges a light flux having the second wavelength λ2emitted from the light source module on an information recording planeof the second optical information recording medium.
 56. The opticalsystem of claim 54, wherein the optical system converges a light fluxhaving the second wavelength λ2 emitted from a light source module, inwhich the second and third light sources are packaged, on an informationrecording plane of the second optical information recording medium andconverges a light flux having the third wavelength λ3 emitted from thelight source module on an information recording plane of the thirdoptical information recording medium.
 57. The optical system of claim52, wherein the optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources.58. The optical system of claim 57, wherein a second magnification m1 inthe case that reproducing and/or recording information is conducted fora second optical information recording medium almost coincides with athird magnification m3 in the case that reproducing and/or recordinginformation is conducted for a third optical information recordingmedium.
 59. The optical system of claim 58, wherein a firstmagnification m1 in the case that reproducing and/or recordinginformation is conducted for a first optical information recordingmedium satisfies the following formula:m1=0
 60. The optical system of claim 57, wherein the optical systemconverges a light flux having the second wavelength λ2 emitted from alight source module, in which the second and third light sources arepackaged, on an information recording plane of the second opticalinformation recording medium and converges a light flux having the thirdwavelength λ3 emitted from the light source module on an informationrecording plane of the third optical information recording medium. 61.The optical system of claim 52, wherein the optical functional zoneincluding an optical axis of the plurality of optical functional zoneshas a superposition type diffractive structure including a plurality ofring-shaped zones which are formed concentrically around an opticalaxis, wherein each ring-shaped zone is composed of a plurality ofstepped sections stepwise, and the first wavelength λ1 and the minimumvalue P of a distance in a direction perpendicular to the optical axisbetween neighboring stepped sections in each ring-shaped zone satisfythe following formulas (30) and (31):0.39 μm<λ1<0.42 μm  (30)P>3 μm  (31)
 62. The optical system of claim 61, wherein the opticalsystem is used to conduct reproducing and/or recording information for athird optical information recording medium equipped with a protectivelayer having a thickness t3 (t3≧t2>t1) by using a light flux having athird wavelength λ3 (λ3>λ2>λ1) emitted from a third light sourcedifferent from the first and second light sources.
 63. The opticalsystem of claim 52, wherein an optical path difference added to atransmitted wave-front by the superposition type diffractive structureis defined by the following arithmetic expression, signs of B₂ and B₄are different from each other,$\varphi_{b} = {{\lambda/\lambda_{B}} \times n \times {\sum\limits_{j = 1}\; {B_{2j}h^{2j}}}}$where λ is a wavelength of an incident light flux, π_(B) is a productionwavelength, h is a height (mm) in a direction perpendicular to theoptical axis, B_(2j) is a optical path difference function coefficient,and n is the diffraction order.
 64. The optical system of claim 63,wherein the optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources.65. The optical system of claim 52, wherein the superposition typediffractive structure is formed within two optical functional zones ofthe plurality of optical functional zones, and wherein the number N ofthe stepped sections in each ring-shaped zone or a depth Δ (μm), in theoptical axis direction, of the stepped sections is different from eachoptical functional zone.
 66. The optical system of claim 65, wherein theoptical system is used to conduct reproducing and/or recordinginformation for a third optical information recording medium equippedwith a protective layer having a thickness t3 (t3≧t2>t1) by using alight flux having a third wavelength λ3 (λ3>λ2>λ1) emitted from a thirdlight source different from the first and second light sources.
 67. Theoptical system of claim 52, wherein on an optical surface of thecorrecting optical system is formed a diffractive structure including aplurality of ring-shaped zones which are formed concentrically around anoptical axis, wherein each of the plurality of ring-shaped zones isdivided by the stepped section to generate a diffractive light ray ofdiffractive order whose absolute value is not small than 1 for the lightflux.
 68. The optical system of claim 67, wherein the optical system isused to conduct reproducing and/or recording information for a thirdoptical information recording medium equipped with a protective layerhaving a thickness t3 (t3≧t2>t1) by using a light flux having a thirdwavelength λ3 (λ3>λ2>1) emitted from a third light source different fromthe first and second light sources.
 69. The optical system of claim 52,wherein on an optical surface of the correcting optical system is formedan optical path difference providing structure having a central regionincluding the optical axis and a plurality of ring-shaped zones dividedwith a stepped section at the outside of the central region.
 70. Theoptical system of claim 69, wherein the optical system is used toconduct reproducing and/or recording information for a third opticalinformation recording medium equipped with a protective layer having athickness t3 (t3≧t2>t1) by using a light flux having a third wavelengthλ3 (λ3>λ2>1) emitted from a third light source different from the firstand second light sources.
 71. A correcting optical system for use in anoptical pickup apparatus in which reproducing and/or recordinginformation is conducted for a first optical information recordingmedium equipped with a protective layer having a thickness t1 by using alight flux having a first wavelength λ1 emitted from a first lightsource and reproducing and/or recording information is conducted for asecond optical information recording medium equipped with a protectivelayer having a thickness t2 (t2≧t1) by using a light flux having asecond wavelength λ2 (λ2>λ1) emitted from a second light source, whereinthe correcting optical system is provided on an optical path betweenboth of the first and second light sources and a light convergingelement to converge a light flux having the first wavelength λ1 emittedfrom the first light source and a light flux having the secondwavelength λ2 emitted from the second light source respectively onto aninformation recording plane of the first and second optical informationrecording mediums; and the correcting optical system comprising: anoptical surface having a plurality of ring-shaped optical functionalzones, and a superposition type diffractive structure is formed on oneof the plurality of optical functional zones such that a plurality ofring-shaped zones are formed concentrically around the optical axis andplural stepped sections shaped stepwise are formed within eachring-shaped zone.
 72. The correcting optical system of claim 71, whereinthe correcting optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources,and is provided between all of the first, second and third light sourcesand the light converging element.
 73. The correcting optical system ofclaim 71, wherein the optical functional zone including an optical axisof the plurality of optical functional zones has a superposition typediffractive structure including a plurality of ring-shaped zones whichare formed concentrically around an optical axis, wherein eachring-shaped zone is composed of a plurality of stepped sectionsstepwise, and the first wavelength 1 and the minimum value P of adistance in a direction perpendicular to the optical axis betweenneighboring stepped sections in each ring-shaped zone satisfy thefollowing formulas (30) and (31):0.39 μm<λ1<0.42 μm  (30)P>3 μm  (31)
 74. The correcting optical system of claim 73, wherein thecorrecting optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources,and is provided between all of the first, second and third light sourcesand the light converging element.
 75. The correcting optical system ofclaim 71, wherein an optical path difference added to a transmittedwave-front by the superposition type diffractive structure is defined bythe following arithmetic expression, signs of B₂ and B₄ are differentfrom each other,$\varphi_{b} = {{\lambda/\lambda_{B}} \times n \times {\sum\limits_{j = 1}\; {B_{2j}h^{2j}}}}$where λ is a wavelength of an incident light flux, λ_(B) is a productionwavelength, h is a height (mm) in a direction perpendicular to theoptical axis, B_(2j) is a optical path difference function coefficient,and n is the diffraction order.
 76. The correcting optical system ofclaim 75, wherein the correcting optical system is used to conductreproducing and/or recording information for a third optical informationrecording medium equipped with a protective layer having a thickness t3(t3≧t2>t1) by using a light flux having a third wavelength λ3 (λ3>λ2>λ1)emitted from a third light source different from the first and secondlight sources, and is provided between all of the first, second andthird light sources and the light converging element.
 77. The correctingoptical system of claim 71, wherein the superposition type diffractivestructure is formed within two optical functional zones of the pluralityof optical functional zones, and wherein the number N of the steppedsections in each ring-shaped zone or a depth Δ(μm), in the optical axisdirection, of the stepped sections is different from each opticalfunctional zone.
 78. The correcting optical system of claim 77, whereinthe correcting optical system is used to conduct reproducing and/orrecording information for a third optical information recording mediumequipped with a protective layer having a thickness t3 (t3≧t2>t1) byusing a light flux having a third wavelength λ3 (λ3>λ2>λ1) emitted froma third light source different from the first and second light sources,and is provided between all of the first, second and third light sourcesand the light converging element.
 79. The correcting optical system ofclaim 71, wherein a superposition type diffractive structure is formedwithin one of the plurality of optical functional zones and thecorrecting optical system further comprises an optical surface having adiffractive structure which includes a plurality of ring-shaped zonesformed concentrically around an optical axis, wherein each of theplurality of ring-shaped zones is divided by a stepped section togenerate a diffractive light ray of diffractive order whose absolutevalue is not small than 1 for the light flux.
 80. The correcting opticalsystem of claim 79, wherein the correcting optical system is used toconduct reproducing and/or recording information for a third opticalinformation recording medium equipped with a protective layer having athickness t3 (t3≧t2>t1) by using a light flux having a third wavelengthλ3 (λ3>λ2>λ1) emitted from a third light source different from the firstand second light sources, and is provided between all of the first,second and third light sources and the light converging element.
 81. Thecorrecting optical system of claim 71, wherein the correcting opticalsystem comprises a optical path difference providing structure toprovide a predetermined optical path difference, and wherein a pluralityof ring-shaped zones are formed continuously around an optical axis onthe optical path difference providing structure and each ring-shapedzone is divided with a stepped section.
 82. The correcting opticalsystem of claim 81, wherein the correcting optical system is used toconduct reproducing and/or recording information for a third opticalinformation recording medium equipped with a protective layer having athickness t3 (t3≧t2>t1) by using a light flux having a third wavelengthλ3 (λ3>λ2>λ1) emitted from a third light source different from the firstand second light sources, and is provided between all of the first,second and third light sources and the light converging element.
 83. Alight converging element for use in an optical pickup apparatus in whichreproducing and/or recording information is conducted for a firstoptical information recording medium equipped with a protective layerhaving a thickness t1 by using a light flux having a first wavelength λ1emitted from a first light source and reproducing and/or recordinginformation is conducted for a second optical information recordingmedium equipped with a protective layer having a thickness t2 (t2≧t1) byusing a light flux having a second wavelength λ2 (λ2>λ1) emitted from asecond light source, comprising: an optical surface of the lightconverging element having a plurality of optical functional zones, and asuperposition type diffractive structure is formed within one of theplurality of optical functional zones such that a plurality ofring-shaped zones are formed around the optical axis and plural steppedsections shaped stepwise are formed within each ring-shaped zone. 84.The light converging element of claim 83, wherein the light convergingelement is used to conduct reproducing and/or recording information fora third optical information recording medium equipped with a protectivelayer having a thickness t3 (t3≧t2>t1) by using a light flux having athird wavelength λ3 (λ3>λ2>1) emitted from a third light sourcedifferent from the first and second light sources.
 85. The lightconverging element of claim 83, wherein a first magnification m1 in thecase that reproducing and/or recording information is conducted for afirst optical information recording medium almost coincides with asecond magnification m2 in the case that reproducing and/or recordinginformation is conducted for a second optical information recordingmedium.
 86. The light converging element of claim 85, wherein the lightconverging element is used to conduct reproducing and/or recordinginformation for a third optical information recording medium equippedwith a protective layer having a thickness t3 (t3≧t2>t1) by using alight flux having a third wavelength λ3 (λ3>λ2>λ1) emitted from a thirdlight source different from the first and second light sources.
 87. Thelight converging element of claim 83, wherein the light convergingelement is used to conduct reproducing and/or recording information fora third optical information recording medium equipped with a protectivelayer having a thickness t3 (t3≧t2>t1) by using a light flux having athird wavelength λ3 (λ3>λ2>λ1) emitted from a third light sourcedifferent from the first and second light sources, the light convergingelement is located at a position to face the first optical informationrecording medium, the second optical information recording medium andthe third optical information recording medium, and a secondmagnification m1 in the case that reproducing and/or recordinginformation is conducted for a second optical information recordingmedium almost coincides with a third magnification m3 in the case thatreproducing and/or recording information is conducted for a thirdoptical information recording medium.
 88. The light converging elementof claim 87, wherein the light converging element is used to conductreproducing and/or recording information for a third optical informationrecording medium equipped with a protective layer having a thickness t3(t3≧t2>t1) by using a light flux having a third wavelength λ3 (λ3>λ2>λ1)emitted from a third light source different from the first and secondlight sources.
 89. The light converging element of claim 83, wherein anoptical functional zone including an optical axis of the plurality ofoptical functional zones has a superposition type diffractive structureincluding a plurality of ring-shaped zones which are formedconcentrically around an optical axis, wherein each ring-shaped zone iscomposed of a plurality of stepped sections stepwise, and the firstwavelength λ1 and the minimum value P of a distance in a directionperpendicular to the optical axis between neighboring stepped sectionsin each ring-shaped zone satisfy the following formulas (30) and (31):0.39 μm<λ1<0.42 μm  (30)P>3 μm  (31)
 90. The light converging element of claim 89, wherein thelight converging element is used to conduct reproducing and/or recordinginformation for a third optical information recording medium equippedwith a protective layer having a thickness t3 (t3≧t2>t1) by using alight flux having a third wavelength λ3 (λ3>λ2>λ1) emitted from a thirdlight source different from the first and second light sources.
 91. Thelight converging element of claim 83, wherein the superposition typediffractive structure is formed within the optical functional zoneincluding the optical axis of the plurality of optical functional zonesand an optical path difference added to a transmitted wave-front by thesuperposition type diffractive structure is defined by the followingarithmetic expression, signs of B₂ and B₄ are different from each other,$\varphi_{b} = {{\lambda/\lambda_{B}} \times n \times {\sum\limits_{j = 1}\; {B_{2j}h^{2j}}}}$where λ is a wavelength of an incident light flux, λ_(B) is a productionwavelength, h is a height (mm) in a direction perpendicular to theoptical axis, B_(2j) is a optical path difference function coefficient,and n is the diffraction order.
 92. The light converging element ofclaim 91, wherein the light converging element is used to conductreproducing and/or recording information for a third optical informationrecording medium equipped with a protective layer having a thickness t3(t3≧t2>t1) by using a light flux having a third wavelength λ3 (λ3>λ2>λ1)emitted from a third light source different from the first and secondlight sources.
 93. The light converging element of claim 83, wherein thesuperposition type diffractive structure is formed within two opticalfunctional zones of the plurality of optical functional zones, andwherein the number N. of the stepped sections in each ring-shaped zoneor a depth Δ (μm), in the optical axis direction, of the steppedsections is different from each optical functional zone.
 94. The lightconverging element of claim 93, wherein the light converging element isused to conduct reproducing and/or recording information for a thirdoptical information recording medium equipped with a protective layerhaving a thickness t3 (t3≧t2>t1) by using a light flux having a thirdwavelength λ3 (λ3>λ2>1) emitted from a third light source different fromthe first and second light sources.
 95. The light converging element ofclaim 83, wherein the superposition type diffractive structure is formedwithin one of the plurality of optical functional zones and thecorrecting optical system further comprises an optical surface having adiffractive structure which includes a plurality of ring-shaped zonesformed concentrically around an optical axis, wherein each of theplurality of ring-shaped zones are divided y a stepped section togenerate a diffractive light ray of diffractive order whose absolutevalue is not small than 1 for the light flux.
 96. The light convergingelement of claim 95, wherein the light converging element is used toconduct reproducing and/or recording information for a third opticalinformation recording medium equipped with a protective layer having athickness t3 (t3≧t2>t1) by using a light flux having a third wavelengthλ3 (λ3>λ2>λ1) emitted from a third light source different from the firstand second light sources.
 97. The light converging element of claim 83,wherein the light converging element comprises a optical path differenceproviding structure to provide a predetermined optical path difference,and wherein a plurality of ring-shaped zones are formed continuouslyaround an optical axis on the optical path difference providingstructure and each ring-shaped zone is divided with a stepped section.98. The light converging element of claim 97, wherein the lightconverging element is used to conduct reproducing and/or recordinginformation for a third optical information recording medium equippedwith a protective layer having a thickness t3 (t3≧t2>t1) by using alight flux having a third wavelength λ3 (λ3>λ2>λ1) emitted from a thirdlight source different from the first and second light sources.
 99. Anoptical pickup apparatus for conducting recording and/or reproducinginformation for plural different recording mediums with pluralwavelength light fluxes, comprising: a first light source to emit alight flux having a first wavelength λ1 for conducting recording and/orreproducing information for a first information recording mediumequipped with a protective substrate having a thickness t1; a secondlight source to emit a light flux having a second wavelength λ2 (λ2>λ1)for conducting recording and/or reproducing information for a secondinformation recording medium equipped with a protective substrate havinga thickness t2 (t2≧t1); a third light source to emit a light flux havinga third wavelength λ3 (λ3>λ2>λ1) for conducting recording and/orreproducing information for a third information recording mediumequipped with a protective substrate having a thickness t3 (t3≧t2); anobjective optical system to converge a light flux having the wavelengthλ1, λ2 or λ3 onto the first, second or third information recordingmedium respectively; a diaphragm; a driving device to drive theobjective system and the diaphragm as one unit in a directionperpendicular to the optical axis; an entering devise to make at leastone light flux among light fluxes having the first, second and thirdwavelengths λ1, λ2 and λ3 enter in not parallel to the optical axis intothe objective optical system; and a coma aberration correcting elementprovided between the objective lens and a light source to emit a lightflux which enters in not parallel to the optical axis into the objectiveoptical system and to reduce a coma aberration generated when theobjective optical system is driven in the direction perpendicular to theoptical axis by the driving device; wherein an optical surface of theobjective optical system has a plurality of optical functional zones,and a superposition type diffractive structure is formed within theoptical functional zone including an optical axis of the plurality ofoptical functional zones such that a plurality of ring-shaped zones areformed around the optical axis and plural stepped sections shapedstepwise are formed within each ring-shaped zone.
 100. The opticalpickup apparatus of claim 99, wherein the second light source and thethird light source are packaged in a light source module.
 101. Anoptical pickup apparatus for conducting recording and/or reproducinginformation for plural different recording mediums with pluralwavelength light fluxes, comprising: a first light source to emit alight flux having a first wavelength λ1 for conducting recording and/orreproducing information for a first information recording mediumequipped with a protective substrate having a thickness t1; a secondlight source to emit a light flux having a second wavelength λ2 (λ2>λ1)for conducting recording and/or reproducing information for a secondinformation recording medium equipped with a protective substrate havinga thickness t2 (t2≧t1); a third light source to emit a light flux havinga third wavelength λ3 (λ3>λ2>λ1) for conducting recording and/orreproducing information for a third information recording mediumequipped with a protective substrate having a thickness t3 (t3≧t2); anobjective optical system to converge a light flux having the wavelengthλ1, λ2 or λ3 onto the first, second or third information recordingmedium respectively, wherein an optical surface of the objective opticalsystem has a plurality of optical functional zones, and a superpositiontype diffractive structure is formed within an optical functional zoneincluding an optical axis of the plurality of optical functional zonessuch that a plurality of ring-shaped zones are formed around the opticalaxis and plural stepped sections shaped stepwise are formed within eachring-shaped zone; an entering device to enter at least two light fluxeswith respective different magnifications into the objective opticalsystem among light fluxes having the first, second and third wavelengthsλ1, λ2 and λ3; an divergent angle converting element having an opticalsurface including a superposition type diffractive structure, whereinthe superposition type diffractive structure includes a plurality ofring-shaped zones which are formed concentrically around an opticalaxis, wherein each ring-shaped zone is composed of a plurality ofstepped section stepwise, the divergent angle converting element toconvert a divergent angle of at least a light flux having one of thefirst, second and third wavelengths λ1, λ2 and λ3; wherein light sourcesto emit at least two light fluxes entering with respective differentmagnifications into the objective optical system among the first, secondand third light sources are packaged in a light source module and thedivergent angle converting element is located on a optical path betweenthe light source module and the objective optical system.
 102. Anoptical pickup apparatus for conducting recording and/or reproducinginformation for plural different recording mediums with pluralwavelength light fluxes, comprising: a first light source to emit alight flux having a first wavelength λ1 for conducting recording and/orreproducing information for a first information recording mediumequipped with a protective substrate having a thickness t1; a secondlight source to emit a light flux having a second wavelength λ2 (λ2>λ1)for conducting recording and/or reproducing information for a secondinformation recording medium equipped with a protective substrate havinga thickness t2 (t2>t1); a third light source to emit a light flux havinga third wavelength λ3 (λ3>λ2>λ1) for conducting recording and/orreproducing information for a third information recording mediumequipped with a protective substrate having a thickness t3 (t3≧t2); adiffractive lens having an optical surface including a superpositiontype diffractive structure, wherein the superposition type diffractivestructure includes a plurality of ring-shaped zones which are formedconcentrically around an optical axis, wherein each ring-shaped zone iscomposed of a plurality of stepped section stepwise, wherein thesuperposition type diffractive structure has a function to providesubstantially no optical path difference to the first and third lightfluxes and to provide an optical path difference only to the secondlight flux; and a light converging element to converge a light fluxhaving the wavelength λ1, λ2 or λ3 having passed through the diffractivelens onto the first, second or third information recording mediumrespectively; wherein the following formula (173) is satisfied:m1≧m2>m3  (173) where m1 is a magnification of an optical systemstructured by the diffractive lens and the light converging element fora light flux having the first wavelength λ1, m2 is a magnification of anoptical system structured by the optical member and the light convergingelement for a light flux having the second wavelength λ2 and m3 is amagnification for a light flux having the third wavelength λ3.
 103. Anoptical pickup apparatus for conducting recording and/or reproducinginformation for plural different recording mediums with pluralwavelength light fluxes, comprising: a first light source to emit alight flux having a first wavelength λ1 for conducting recording and/orreproducing information for a first information recording mediumequipped with a protective substrate having a thickness t1; a secondlight source to emit a light flux having a second wavelength λ2 (λ2>λ1)for conducting recording and/or reproducing information for a secondinformation recording medium equipped with a protective substrate havinga thickness t2 (t2≧t1); a third light source to emit a light flux havinga third wavelength λ3 (λ3>λ2>λ1) for conducting recording and/orreproducing information for a third information recording mediumequipped with a protective substrate having a thickness t3 (t3≧t2); alight converging element to converge a light flux having the wavelengthλ1, λ2 or λ3 onto the first, second or third information recordingmedium respectively; a correcting optical system having an opticalsurface including a predetermined stepped structure; and a sphericalaberration correcting member; wherein the correcting optical system hasa function to correct a spherical aberration generated by the lightconverging element due to a difference between the first wavelength λ1and the second wavelength λ2 and/or a spherical aberration caused due toa difference between t1 and t2 and the spherical aberration correctingmember has a function to correct a spherical aberration caused due to adifference between t1 and t3.
 104. The optical pickup apparatus of claim103, wherein the stepped structure is one of a superposition typediffractive structure, a diffractive structure and an optical pathdifference providing structure.
 105. The optical pickup apparatus ofclaim 104, wherein an optical path difference provided to the firstlight flux by the stepped structure is multiplied the first wavelengthwith an integer.
 106. The optical pickup apparatus of claim 105, whereinan optical path difference provided to the first light flux by thestepped structure is multiplied the first wavelength with an evennumber.
 107. The optical pickup apparatus of claim 106, furthercomprising: a second correcting optical system having an optical surfaceincluding a diffractive structure and an optical path differenceprovided to the first light flux by the diffractive structure ismultiplied the first wavelength with an odd number.
 108. The opticalpickup apparatus of claim 106, further comprising: a second correctingoptical system having an optical surface including a optical pathdifference providing structure and an optical path difference providedto the first light flux by the optical path difference providing ismultiplied the first wavelength with an odd number.
 109. The opticalpickup apparatus of claim 103, wherein a magnification m1 of an opticalsystem structured by the light converging element and the aberrationcorrecting element for a light flux having the first wavelength λ1almost coincides with a second magnification m2 for a light flux havingthe second wavelength λ2.
 110. The optical pickup apparatus of claim107, wherein a magnification m1 of an optical system structured by thelight converging element and the aberration correcting element for alight flux having the first wavelength λ1 almost coincides with a secondmagnification m2 for a light flux having the second wavelength λ2. 111.The optical pickup apparatus of claim 108, wherein a magnification m1 ofan optical system structured by the light converging element and theaberration correcting element for a light flux having the firstwavelength λ1 almost coincides with a second magnification m2 for alight flux having the second wavelength λ2.
 112. The optical pickupapparatus of claim 103, wherein the light converging element isoptimized in terms of a spherical aberration for the first wavelength λ1and the protective substrate having the thickness t1.
 113. The opticalpickup apparatus of claim 110, wherein the light converging element isoptimized in terms of a spherical aberration for the first wavelength λ1and the protective substrate having the thickness t1.
 114. The opticalpickup apparatus of claim 111, wherein the light converging element isoptimized in terms of a spherical aberration for the first wavelength λ1and the protective substrate having the thickness t1.
 115. The opticalpickup apparatus of claim 103, wherein the light converging element andthe aberration correcting element is supported such that a relativepositional relationship therebetween is not changed.
 116. The opticalpickup apparatus of claim 113, wherein the light converging element andthe aberration correcting element is supported such that a relativepositional relationship therebetween is not changed.
 117. The opticalpickup apparatus of claim 114, wherein the light converging element andthe aberration correcting element is supported such that a relativepositional relationship therebetween is not changed.
 118. The opticalpickup apparatus of claim 103, wherein the spherical aberrationcorrecting member is a liquid crystal phase controlling elementcomprising a liquid crystal layer to cause a phase change for atransmitting light flux due to an application of a voltage and electrodelayers to face to each other so as to apply a voltage to the liquidcrystal layer, and the liquid crystal phase controlling element correctsa spherical aberration due to a difference between the thickness t1 andthe thickness t3 by conducting a phase control for the third light flux.119. The optical pickup apparatus of claim 116, wherein the sphericalaberration correcting member is a liquid crystal phase controllingelement comprising a liquid crystal layer to cause a phase change for atransmitting light flux due to an application of a voltage and electrodelayers to face to each other so as to apply a voltage to the liquidcrystal layer, and the liquid crystal phase controlling element correctsa spherical aberration due to a difference between the thickness t1 andthe thickness t3 by conducting a phase control for the third light flux.120. The optical pickup apparatus of claim 117, wherein the sphericalaberration correcting member is a liquid crystal phase controllingelement comprising a liquid crystal layer to cause a phase change for atransmitting light flux due to an application of a voltage and electrodelayers to face to each other so as to apply a voltage to the liquidcrystal layer, and the liquid crystal phase controlling element correctsa spherical aberration due to a difference between the thickness t1 andthe thickness t3 by conducting a phase control for the third light flux.121. The optical pickup apparatus of claim 118, wherein the liquidcrystal phase controlling element selectively conducts only a phasecontrol for the third light flux.
 122. The optical pickup apparatus ofclaim 119, wherein the liquid crystal phase controlling elementselectively conducts only a phase control for the third light flux. 123.The optical pickup apparatus of claim 120, wherein the liquid crystalphase controlling element selectively conducts only a phase control forthe third light flux.
 124. The optical pickup apparatus of claim 103,wherein the spherical aberration correcting member is a movable lensunit comprising an actuator and a movable lens group capable of beingmoved in the optical axis direction by the actuator, and the movablelens unit corrects a spherical aberration due to a difference betweenthe thickness t1 and the thickness t3 by changing a magnification of thelight converging element.
 125. The optical pickup apparatus of claim116, wherein the spherical aberration correcting member is a movablelens unit comprising an actuator and a movable lens group capable ofbeing moved in the optical axis direction by the actuator, and themovable lens unit corrects a spherical aberration due to a differencebetween the thickness t1 and the thickness t3 by changing amagnification of the light converging element.
 126. The optical pickupapparatus of claim 117, wherein the spherical aberration correctingmember is a movable lens unit comprising an actuator and a movable lensgroup capable of being moved in the optical axis direction by theactuator, and the movable lens unit corrects a spherical aberration dueto a difference between the thickness t1 and the thickness t3 bychanging a magnification of the light converging element.
 127. Theoptical pickup apparatus of claim 125, wherein a magnification m3 of thelight converging element for the third wavelength λ3 satisfies thefollowing formula (177):−0.15<m3<−0.02  (177)
 128. The optical pickup apparatus of claim 126,wherein a magnification m3 of the light converging element for the thirdwavelength λ3 satisfies the following formula (177):−0.15<m3<−0.02  (177)
 129. The optical pickup apparatus of claim 103,wherein at least two light sources among the first, second and thirdlight sources are made in one body.
 130. The optical pickup apparatus ofclaim 127, wherein at least two light sources among the first, secondand third light sources are made in one body.
 131. The optical pickupapparatus of claim 128, wherein at least two light sources among thefirst, second and third light sources are made in one body.
 132. Theoptical pickup apparatus of claim 129, wherein all of the first, secondand third light sources are made in one body.
 133. The optical pickupapparatus of claim 130, wherein all of the first, second and third lightsources are made in one body.
 134. The optical pickup apparatus of claim131, wherein all of the first, second and third light sources are madein one body. 135-150. (canceled)